California: Individual County Chronologies

California Atlas of Historical County Boundaries

John H. Long, Editor; Peggy Tuck Sinko, Historical Compiler; Laura Rico-Beck, GIS Specialist and Digital Compiler; Peter Siczewicz, ArcIMS Interactive Map Designer; Emily Kelley, Research Associate; Robert Will, Cartographic Assistant

Copyright The Newberry Library 2003

ALAMEDA

25 Mar 1853
ALAMEDA created from CONTRA COSTA and SANTA CLARA. (Calif. Stats. 1853, 4th sess., ch. 41/pp. 56–59)
30 Mar 1874
ALAMEDA gained small area in San Francisco Bay from SAN FRANCISCO; placed all of the Central Pacific Railroad Wharf in ALAMEDA. The wharf was removed in 1919 [change too small to display on interactive map; shapefile users see small_changes 1874_pt. for location]. (Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, pp. 168–170; Coy, 62–63)
14 Mar 1878
Boundary between ALAMEDA and SAN MATEO in San Francisco Bay was adjusted [not mapped]. (Calif. Stats. 1877, 22d sess., Acts Amendatory of the Political Code, ch. 197/p. 71)
14 Jan 1958
ALAMEDA gained small area from CONTRA COSTA [change too small to display on interactive map; shapefile users see small_changes 1958_pt. for location]. (Coy, 338–339)
02 Nov 1971
ALAMEDA lost small areas to SANTA CLARA [change too small to display on interactive map; shapefile users see small_changes 1971_pt. for location]. (Coy, 338, 343)
01 Sep 1992
ALAMEDA gained small area from CONTRA COSTA. Ordinance passed 11 August 1992; effective 1 September 1992 [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Minutes of the Board of Supervisors, Alameda County, 11 August 1992, ordinance 92–57)
11 Oct 1993
ALAMEDA boundaries restated to incorporate 1 September 1992 change [no change]. (Calif. Stats. 1993–1994, reg. sess., ch. 1195, sec. 2.5/p. 6853)
04 Oct 1995
ALAMEDA lost small area to CONTRA COSTA [change too small to display on interactive map; shapefile users see small_changes 1995_pt. for location]. (Calif. Stats. 1995, reg. sess., ch. 529, sec. 3 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002)
19 Aug 1996
ALAMEDA boundary clarified [no discernible change]. (Calif. Stats. 1996, reg. sess., ch. 400, sec. 4 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002)

ALPINE

16 Mar 1864
ALPINE created from AMADOR, CALAVERAS, EL DORADO, MONO, and TUOLUMNE. (Calif. Stats. 1863–1864, 15th sess., ch. 180/pp. 178–182)
17 Nov 1995
ALPINE gained small area from AMADOR. Ordinance passed 3 October 1995; effective 17 November 1995 [change too small to display on interactive map; shapefile users see small_changes 1995_pt. for location]. (Minutes of the Board of Supervisors, Amador County, 3 October 1995, ordinance 1390)

AMADOR

14 Jun 1854
AMADOR created from CALAVERAS. Act passed 11 May 1854; referendum for or against creation of the new county held 14 June 1854. (Calif. Stats. 1854, 5th sess., ch. 42/pp. 45–48)
16 Apr 1855
AMADOR gained from EL DORADO. (Calif. Stats. 1855, 6th sess., ch. 92/p. 113)
23 Apr 1855
AMADOR boundaries redefined [no change]. (Calif. Stats. 1855, 6th sess., ch. 113/p. 134–135)
25 Apr 1857
AMADOR exchanged with EL DORADO. (Calif. Stats. 1857, 8th sess., ch. 220/p. 251)
08 Apr 1863
AMADOR gained from EL DORADO. (Calif. Stats. 1863, 14th sess., ch. 170/p. 231)
16 Mar 1864
AMADOR lost to creation of ALPINE. (Calif. Stats. 1863–1864, 15th sess., ch. 180/pp. 178–182)
02 Mar 1866
AMADOR lost to MONO the remnant of territory that was left separate from AMADOR by the creation of ALPINE. (Calif. Stats. 1865, 16th sess., ch. 161/p. 144)
30 Jun 1991
AMADOR gained small area from EL DORADO. Ordinance passed 25 June 1991; effective 30 June 1991[change too small to display on interactive map; shapefile users see small_changes 1991_pt. for location]. (Minutes of the Board of Supervisors, El Dorado County, 25 June 1991, resolution 211–91; Minutes of the Board of Supervisors, Amador County, 12 June 1990, resolution 90–182)
17 Nov 1995
AMADOR lost small area to ALPINE. Ordinance passed 3 October 1995; effective 17 November 1995 [change too small to display on interactive map; shapefile users see small_changes 1995_pt. for location]. (Minutes of the Board of Supervisors, Amador County, 3 October 1995, ordinance 1390)

BRANCIFORTE (see SANTA CRUZ)

BUENA VISTA (proposed)

30 Apr 1855
Legislature authorized creation of BUENA VISTA (proposed) from TULARE; creation did not take effect. (Calif. Stats. 1855, 6th sess., ch. 161/pp. 203–205; Coy, 15–16)
16 Apr 1856
Legislature authorized BUENA VISTA (proposed) to gain from TULARE, even though the creation of BUENA VISTA (authorized 30 April 1855) had never gone into effect. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1856, 7th sess., ch. 81/p. 96)

BUTTE

18 Feb 1850
BUTTE created from non-county area. COLUSI (now COLUSA) not fully organized, attached to BUTTE "for judicial purposes." (Calif. Stats. 1849, 1st sess., ch. 15, sec. 21/p. 62)
10 Jan 1851
COLUSI (now COLUSA) fully organized, detached from BUTTE. (Rogers, 57–61)
25 Apr 1851
BUTTE gained from SUTTER, lost small area to SHASTA. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 21/p. 177)
03 May 1852
BUTTE exchanged with SUTTER. (Calif. Stats. 1852, 3d sess., ch. 149/p. 237)
19 Mar 1853
BUTTE boundaries clarified [no change]. (Calif. Stats. 1853, 4th sess., ch. 37/p. 53)
31 Mar 1854
BUTTE lost to SUTTER. (Calif. Stats. 1854, 5th sess., ch. 16/p. 26)
01 Apr 1854
BUTTE lost to creation of PLUMAS. (Calif. Stats. 1854, 5th sess., ch. 1/pp. 129–131)
09 Apr 1856
BUTTE lost to creation of TEHAMA. (Calif. Stats. 1856, 7th sess., ch. 100/pp. 118–119)
19 Apr 1856
BUTTE lost to COLUSI (now COLUSA). (Calif. Stats. 1856, 7th sess., ch. 105/p. 124)
21 Apr 1856
BUTTE lost to SUTTER. (Calif. Stats. 1856, 7th sess., ch. 150/p. 231)
19 Apr 1859
BUTTE gained from TEHAMA. (Calif. Stats. 1859, 10th sess., ch. 322/p. 359)
22 Mar 1860
BUTTE lost small area in village of Strawberry Valley to YUBA [change too small to display on interactive map; shapefile users see small_changes 1860_pt. for location]. (Calif. Stats. 1860, 11th sess., ch. 145/p. 115)
15 Apr 1861
BUTTE lost small area at Woodville to YUBA [change too small to display on interactive map; shapefile users see small_changes 1861_pt. for location]. (Calif. Stats. 1861, 12th sess., ch. 166/p. 167)
01 Apr 1864
BUTTE lost to SUTTER. (Calif. Stats. 1863–1864, 15th sess., ch. 292/p. 301)
01 Jan 1873
BUTTE gained from COLUSA. (Political Code 1872, 1: secs. 3916, 3922/pp. 119, 123–124)
07 Mar 1874
BUTTE boundaries clarified [no change]. (Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, p. 167)
25 Feb 1897
BUTTE exchanged with YUBA. (Calif. Stats. 1897, 32d sess., ch. 26/p. 22)
23 Mar 1901
BUTTE exchanged with PLUMAS. (Calif. Stats. 1901, 34th sess., ch. 146/pp. 549–551)
08 Aug 1915
BUTTE gained small area in section 3, township 19 north, range 1 east from GLENN [change too small to display on interactive map; shapefile users see small_changes 1915_pt. for location]. (Calif. Stats. 1915, 41st sess., ch. 532/p. 898)
20 Nov 1944
BUTTE exchanged with TEHAMA. (Coy, 339, 345)

CALAVERAS

18 Feb 1850
CALAVERAS created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 25/p. 63)
18 Apr 1850
CALAVERAS boundaries clarified [no change]. (Calif. Stats. 1849, 1st sess., ch. 111/pp. 262–263)
25 Apr 1851
CALAVERAS boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 13/p. 175)
14 Jun 1854
CALAVERAS lost to creation of AMADOR. Act passed 11 May 1854; referendum for or against creation of the new county held 14 June 1854. (Calif. Stats. 1854, 5th sess., ch. 42/pp. 45–48)
19 Apr 1856
CALAVERAS lost to creation of FREZNO (now FRESNO). (Calif. Stats. 1856, 7th sess., ch. 127/pp. 183)
24 Apr 1861
CALAVERAS lost to creation of MONO. (Calif. Stats. 1861, 12th sess., ch. 233/pp. 235–236)
16 Mar 1864
CALAVERAS lost to creation of ALPINE. (Calif. Stats. 1863–1864, 15th sess., ch. 180/pp. 178–182)

COLUSA

18 Feb 1850
COLUSI (now COLUSA) created from non-county area; COLUSI not fully organized, attached to BUTTE "for judicial purposes." (Calif. Stats. 1849, 1st sess., ch. 15, sec. 22/p. 62)
10 Jan 1851
COLUSI (now COLUSA) fully organized, detached from BUTTE. (Rogers, 57–61)
25 Apr 1851
COLUSI (now COLUSA) gained from YOLO, lost to SHASTA. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 29/p. 179)
09 Apr 1856
COLUSI (now COLUSA) lost to creation of TEHAMA. (Calif. Stats. 1856, 7th sess., ch. 100/pp. 118–119)
19 Apr 1856
COLUSI (now COLUSA) gained from BUTTE, SUTTER, and YOLO. (Calif. Stats. 1856, 7th sess., ch. 105/p. 124)
19 Feb 1857
COLUSI (now COLUSA) gained from TEHAMA. (Calif. Stats. 1857, 8th sess., ch. 37/p. 25)
by Jan 1859
The spelling of "COLUSI" changed to "COLUSA." (Calif. Stats. 1859, 10th sess.; [Green], 44–45)
19 Apr 1859
COLUSA lost to TEHAMA. (Calif. Stats. 1859, 10th sess., ch. 322/p. 359)
24 Mar 1868
COLUSA lost to LAKE. (Calif. Stats. 1867, 17th sess., ch. 257/p. 269)
01 Jan 1873
COLUSA gained from TEHAMA, lost to BUTTE. (Political Code 1872, 1: secs. 3915–3916, 3922/pp. 118–119, 123–124)
31 Mar 1891
COLUSA lost small area to SUTTER [change too small to display on interactive map; shapefile users see small_changes 1891_pt. for location]. (Calif. Stats. 1891, 29th sess., ch. 240/p. 455)
05 May 1891
COLUSA lost to creation of GLENN. Act passed 11 March 1891; referendum for or against creation of the new county held 5 May 1891. (Calif. Stats. 1891, 29th sess., ch. 94/pp. 98–101)
11 Mar 1893
COLUSA gained from GLENN. (Calif. Stats. 1893, 30th sess., ch. 141/p. 158)
13 Mar 1909
Boundary of LAKE with COLUSA and MENDOCINO redefined [no change]. (Calif. Stats. 1909, 38th sess., ch. 211/pp. 326–328)

COLUSI (see COLUSA)

CONTRA COSTA

18 Feb 1850
CONTRA COSTA created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 10/p. 60)
05 Apr 1850
CONTRA COSTA boundaries clarified [no change]. (Calif. Stats. 1849, 1st sess., ch. 61, sec. 4/p. 156)
25 Apr 1851
CONTRA COSTA boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 10/p. 174)
14 Feb 1852
CONTRA COSTA lost to SAN JOAQUIN. (Calif. Stats. 1852, 3d sess., chs. 105–106/pp. 178–180; Purcell, 250)
25 Mar 1853
CONTRA COSTA lost to creation of ALAMEDA, and lost small remnant to SANTA CLARA. (Calif. Stats. 1853, 4th sess., ch. 41/pp. 56–59)
26 Mar 1868
CONTRA COSTA gained the Brothers Islands from MARIN. (Calif. Stats. 1867, 17th sess., ch. 305/p. 347)
14 Jan 1958
CONTRA COSTA lost small area to ALAMEDA [change too small to display on interactive map; shapefile users see small_changes 1958_pt. for location]. (Coy, 338–339)
01 Sep 1992
CONTRA COSTA lost small area to ALAMEDA. Ordinance passed 11 August 1992; effective 1 September 1992 [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Minutes of the Board of Supervisors, Alameda County, 11 August 1992, ordinance 92–57)
04 Oct 1995
CONTRA COSTA gained small area from ALAMEDA [change too small to display on interactive map; shapefile users see small_changes 1995_pt. for location]. (Calif. Stats. 1995, reg. sess., ch. 529, sec. 3 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002)

COSO (proposed)

04 Apr 1864
Legislature authorized creation of COSO from MONO and TULARE; creation did not take effect [see creation of INYO, 22 March 1866]. (Calif. Stats. 1863–1864, 15th sess., ch. 470/pp. 528–530)

DEL NORTE

02 Mar 1857
DEL NORTE created from KLAMATH (extinct) and a small area of SISKIYOU. (Calif. Stats. 1857, 8th sess., ch. 52/pp. 35–36)
11 Feb 1858
DEL NORTE boundaries clarified [no change]. (Calif. Stats. 1858, 9th sess., ch. 23/p. 21)
01 Jan 1873
DEL NORTE exchanged with SISKIYOU. (Political Code 1872, 1: secs. 3909–3910, 3913/pp. 113–115, 117)
11 Mar 1887
DEL NORTE exchanged with SISKIYOU. (Calif. Stats. 1887, 27th sess., ch. 88/pp. 105–107)
23 Mar 1901
DEL NORTE exchanged with HUMBOLDT. (Calif. Stats. 1901, 34th sess., ch. 193/p. 600)

Disputed Area

18 Feb 1850
Area between BRANCIFORTE (now SANTA CRUZ) and SAN FRANCISCO was in dispute. Both counties claimed the area. (Calif. Stats. 1849, 1st sess., ch. 15, secs. 7–8/pp. 59–60; Stanger, 88)
01 Jul 1856
SAN MATEO created from SAN FRANCISCO; SAN MATEO boundary with SANTA CRUZ was in dispute [see 18 February 1850]. Dispute ended 18 April 1857 when SAN MATEO gained control over the area. (Calif. Stats. 1856, 7th sess., ch. 125/pp. 145–146, 176–178)

EL DORADO

18 Feb 1850
EL DORADO created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 18/pp. 61–62)
25 Apr 1851
EL DORADO boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 16/p. 176)
16 Apr 1855
EL DORADO lost to AMADOR. (Calif. Stats. 1855, 6th sess., ch. 92/p. 113)
25 Apr 1857
EL DORADO exchanged with AMADOR. (Calif. Stats. 1857, 8th sess., ch. 220/p. 251)
08 Apr 1863
EL DORADO lost to AMADOR. (Calif. Stats. 1863, 14th sess., ch. 170/p. 231)
20 Apr 1863
EL DORADO gained from PLACER. (Calif. Stats. 1863, 14th sess., ch. 263/p. 349)
16 Mar 1864
EL DORADO lost to creation of ALPINE. (Calif. Stats. 1863–1864, 15th sess., ch. 180/pp. 178–182)
10 Aug 1913
EL DORADO exchanged with PLACER. (Calif. Stats. 1913, 40th sess., chs. 315–316/pp. 603–605)
30 Jun 1991
EL DORADO lost small area to AMADOR. Ordinance passed 25 June 1991; effective 30 June 1991 [change too small to display on interactive map; shapefile users see small_changes 1991_pt. for location]. (Minutes of the Board of Supervisors, El Dorado County, 25 June 1991, resolution 211–91; Minutes of the Board of Supervisors, Amador County, 12 June 1990, resolution 90–182)

FRESNO

19 Apr 1856
FREZNO (now FRESNO) created from CALAVERAS, MARIPOSA, MERCED, TULARE, and TUOLUMNE. (Calif. Stats. 1856, 7th sess., ch. 127/pp. 183)
11 Apr 1859
FREZNO (now FRESNO) lost to TUOLUMNE. (Calif. Stats. 1859, 10th sess., ch. 204/p. 213)
24 Apr 1861
FREZNO (now FRESNO) lost to creation of MONO. (Calif. Stats. 1861, 12th sess., ch. 233/pp. 235–236)
by Apr 1862
The phonetic spelling of "FREZNO" changed to "FRESNO." (Calif. Stats. 1863, 13th sess.; Gudde, 138)
29 Mar 1870
FRESNO lost to MARIPOSA. (Calif. Stats. 1869, 18th sess., ch. 341/p. 449)
01 Apr 1872
FRESNO gained from MARIPOSA. (Calif. Stats. 1871, 19th sess., ch. 602/p. 891)
11 Feb 1874
Boundary between FRESNO and MARIPOSA redefined [no change]. (Calif. Stats. 1873, 20th sess., ch. 88/p. 100)
27 Mar 1874
FRESNO exchanged with TULARE. (Calif. Stats. 1873, 20th sess., ch. 468/p. 700)
23 Mar 1876
FRESNO exchanged with TULARE. (Calif. Stats. 1875, 21st sess., ch. 301/p. 397)
11 Mar 1887
FRESNO lost to SAN BENITO. (Calif. Stats. 1887, 27th sess., ch. 86/p.103)
16 May 1893
FRESNO lost to creation of MADERA. Act passed 11 March 1893; referendum for or against creation of new county held 16 May 1893. (Calif. Stats. 1893, 30th sess., ch. 143/pp. 168–172; California USGenWeb Project, Madera County, http://www.cagenweb.com/madera/MadHistory.html, 17 July 2002; "Mariposa County v. Madera County," in Calif. Rpts., 142:50–58)
14 Mar 1907
Legislature authorized KINGS to gain from FRESNO, dependent on local referendum. Referendum failed [no change]. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1907, 37th sess., ch. 214/pp. 260–263; Coy, 51–52; "Wheeler v. Herbert," in Calif. Rpts., 152:224–241)
12 Apr 1909
FRESNO lost to KINGS. (Calif. Stats. 1909, 38th sess., ch. 483/pp. 827–829)
31 Dec 1986
FRESNO gained small area from TULARE. Ordinance passed 18 November 1986; effective 31 December 1986 [change too small to display on interactive map; shapefile users see small_changes 1986_pt. for location]. (Minutes of the Board of Supervisors, Tulare County, 18 November 1986, ordinance 2745)
30 Sep 1991
FRESNO exchanged small areas with TULARE. Ordinance passed 3 September 1991; effective 30 September 1991 [change too small to display on interactive map; shapefile users see small_changes 1991_pt. for location]. (Minutes of the Board of Supervisors, Tulare County, 3 September 1991, ordinance 2970)

FREZNO (see FRESNO)

GLENN

05 May 1891
GLENN created from COLUSA. Act passed 11 March 1891; referendum for or against creation of the new county held 5 May 1891. (Calif. Stats. 1891, 29th sess., ch. 94/pp. 98–101)
11 Mar 1893
GLENN lost to COLUSA. (Calif. Stats. 1893, 30th sess., ch. 141/p. 158)
08 Mar 1907
GLENN gained from MENDOCINO. (Calif. Stats. 1907, 37th sess., ch. 113/p. 135)
13 Mar 1909
GLENN exchanged with LAKE. (Calif. Stats. 1909, 38th sess., ch. 211, sec. 2/p. 327)
08 Aug 1915
GLENN lost small area in section 3, township 19 north, range 1 east to BUTTE [change too small to display on interactive map; shapefile users see small_changes 1915_pt. for location]. (Calif. Stats. 1915, 41st sess., ch. 532/p. 898)

HUMBOLDT

12 May 1853
HUMBOLDT created from TRINITY. (Calif. Stats. 1853, 4th sess., ch. 114/pp. 161–164)
11 Mar 1859
HUMBOLDT lost to MENDOCINO. (Calif. Stats. 1859, 10th sess., ch. 108/pp. 98–99)
28 Apr 1860
HUMBOLDT gained from MENDOCINO. (Calif. Stats. 1860, 11th sess., ch. 340/p. 334)
11 Feb 1862
HUMBOLDT boundaries redefined [no change]. (Calif Laws 1862, 13th sess., ch. 11/p. 6)
30 May 1874
HUMBOLDT gained part of KLAMATH; KLAMATH eliminated. Act passed 28 March 1874; referendum for annexation of KLAMATH held 30 May 1874. (Calif. Stats. 1873, 20th sess., ch. 520/pp. 755–758; Kasch, 270–272)
23 Mar 1901
HUMBOLDT exchanged with DEL NORTE, lost small area to SISKIYOU. (Calif. Stats. 1901, 34th sess., ch. 193/p. 600)

IMPERIAL

12 Aug 1907
IMPERIAL created from SAN DIEGO. (Coy, 50–51; Farr, 18–19)
16 Jun 1967
IMPERIAL boundaries redefined to more precisely define the boundary between IMPERIAL and the State of Arizona [no discernible change]. (Calif. Stats. 1967, reg. sess., ch. 339/pp. 1536–1537; Coy, 339)

INYO

22 Mar 1866
INYO created from MONO and TULARE. INYO boundaries were identical to those of COSO (proposed) [see 4 April 1864]. (Calif. Stats. 1865, 16th sess., ch. 316/pp. 355–358)
28 Mar 1870
INYO gained from MONO. (Calif. Stats. 1869, 18th sess., ch. 323/p. 421)
01 Jan 1873
INYO gained from KERN and SAN BERNARDINO. (Political Code 1872, 1: secs. 3941–3943/pp. 139–140)
19 Sep 1947
Boundary between INYO and SAN BERNARDINO placed in dispute. Section 23136 of Political Code was revised to authorize SAN BERNARDINO to gain from INYO a strip of territory one and one-half miles wide between the San Bernardino Meridian and the state line. The companion description of INYO boundaries in section 23114 authorized no such change [no change]. (Calif. Stats. 1947, reg. sess., ch. 424, secs. 23114, 23136/pp. 1050, 1068)
11 Sep 1957
INYO lost small area to SAN BERNARDINO; boundaries of INYO and SAN BERNARDINO clarified, ending boundary dispute dating from 1947. (Calif. Stats. 1957, reg. sess., ch. 2382/p. 4119)
1972
In 1972, boundary between INYO and SAN BERNARDINO was adjusted [precise location unknown, not mapped]. (Correspondence, California State Board of Equalization, 25 July 2002)

KERN

02 Apr 1866
KERN created from LOS ANGELES and TULARE. (Calif. Stats. 1865, 16th sess., ch. 569/pp. 796–798)
10 Feb 1868
KERN gained from TULARE. (Calif. Stats. 1867, 17th sess., ch. 43/p. 40)
01 Jan 1873
KERN lost to INYO and TULARE. Boundary with VENTURA adjusted to run partially on public land survey lines. (Political Code 1872, 1: secs. 3940–3942/pp. 138–139)
14 Mar 1885
KERN exchanged with SAN LUIS OBISPO. (Calif. Stats. 1885, 26th sess., ch. 149/pp. 139–141)
27 Jul 1917
KERN lost to SAN BERNARDINO. (Calif. Stats. 1917, 42d sess., ch. 205/p. 301)
23 Jul 1919
KERN gained from VENTURA when boundary was adjusted to run on public land survey lines. The California Supreme Court declared this chapter unconstitutional on 19 February 1920, but this particular change appears to have remained in effect; change confirmed in 1923 by reenactment of the 1919 law. (Calif. Stats. 1919, 43d sess., ch. 470, secs. 3923, 3964/pp. 870, 908–909; "Mundell v. Lyons," in Calif. Rpts., 182:289–293; Calif. Laws 1923, 45th sess., ch. 160, secs. 16, 57/pp. 336, 373)
16 May 1923
KERN boundaries redefined; see 23 July 1919 [no change]. (Calif. Laws 1923, 45th sess., ch. 160, secs. 16, 57/pp. 336, 373)
13 May 1963
KERN exchanged small areas with SAN BERNARDINO. (Coy, 340, 342; correspondence, California Board of Equalization, 25 July 2002)
31 Dec 1986
KERN gained small area from VENTURA [precise location unknown, not mapped]. (Minutes of the Board of Supervisors, Kern County, 4 November 1986, ordinance G–4345)
10 Jun 1991
KERN gained from VENTURA. (Calif. Stats. 1991–1992, reg. sess., ch. 51/p. 150)

KINGS

23 May 1893
KINGS created from TULARE. Act passed 22 March 1893; referendum for or against creation of new county held 23 May 1893. (Calif. Stats. 1893, 30th sess., ch. 150/pp. 176–181; Kings County History, http://calflytech.com/kingshistory.html, 18 July 2002)
14 Mar 1907
Legislature authorized KINGS to gain from FRESNO, dependent on local referendum. Referendum failed [no change]. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1907, 37th sess., ch. 214/pp. 260–263; Coy, 51–52; "Wheeler v. Herbert," in Calif. Rpts., 152:224–241)
12 Apr 1909
KINGS gained from FRESNO. (Calif. Stats. 1909, 38th sess., ch. 483/pp. 827–829)

KLAMATH (extinct)

25 Apr 1851
KLAMATH (extinct) created from TRINITY. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 31/p. 180)
22 Mar 1852
KLAMATH (extinct) lost to creation of SISKIYOU. (Calif. Stats. 1852, 3d sess., ch. 146/pp. 233–235)
30 Apr 1855
KLAMATH (extinct) lost to TRINITY. (Calif. Stats. 1855, 6th sess., ch. 156/p. 200)
02 Mar 1857
KLAMATH (extinct) lost to creation of DEL NORTE. (Calif. Stats. 1857, 8th sess., ch. 52/pp. 35–36)
30 May 1874
KLAMATH lost all territory to HUMBOLDT and SISKIYOU; KLAMATH eliminated. Act passed 28 March 1874; referendum for annexation of KLAMATH held 30 May 1874. (Calif. Stats. 1873, 20th sess., ch. 520/pp. 755–758; Kasch, 270–272)

LAKE

20 May 1861
LAKE created from NAPA. (Calif. Stats. 1861, 12th sess., ch. 498/pp. 560–561)
29 Feb 1864
LAKE gained from MENDOCINO and NAPA. (Calif. Stats. 1863–1864, 15th sess., ch. 122/p. 111)
24 Mar 1868
LAKE gained from COLUSA, NAPA, and YOLO. (Calif. Stats. 1867, 17th sess., ch. 257/p. 269)
08 Mar 1872
LAKE lost to NAPA. (Calif. Stats. 1871, 19th sess., ch. 229/p. 305)
08 Mar 1907
LAKE lost to MENDOCINO. (Calif. Stats. 1907, 37th sess., ch. 113/p. 135)
13 Mar 1909
LAKE exchanged with GLENN; boundary of LAKE with COLUSA and MENDOCINO redefined [no change]. (Calif. Stats. 1909, 38th sess., ch. 211/pp. 326–328)
31 Jul 1917
LAKE exchanged with MENDOCINO. (Calif. Stats. 1917, 42d sess., ch. 779/pp. 1635–1640)

LASSEN

01 Apr 1864
LASSEN created from PLUMAS and SHASTA. (Calif. Stats. 1863–1864, 15th sess., ch. 261/pp. 264–269)
26 Mar 1866
LASSEN boundaries clarified [no change]. (Calif. Stats. 1865, 16th sess., ch. 371/p. 453)
01 Jan 1873
LASSEN gained from PLUMAS. (Political Code 1872, 1: secs. 3912, 3920/pp. 115–116, 122–123)
16 Mar 1874
LASSEN lost small area to SIERRA when boundary was set on public land survey lines. (Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, p. 166)
14 Mar 1899
LASSEN gained from SHASTA. (Calif. Stats. 1899, 33d sess., ch. 82/p. 98)
28 Feb 1901
LASSEN exchanged with PLUMAS. (Calif. Stats. 1901, 34th sess., ch. 61/pp. 76–80)

LOS ANGELES

18 Feb 1850
LOS ANGELES created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 3/p. 59)
25 Apr 1851
LOS ANGELES gained from MARIPOSA, exchanged with SAN DIEGO and SANTA BARBARA. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 3/p. 172)
26 Apr 1853
LOS ANGELES lost to creation of SAN BERNARDINO. (Calif. Stats. 1853, 4th sess., ch. 78/pp. 119–123)
26 Mar 1856
LOS ANGELES boundaries redefined [no change]. (Calif. Stats. 1856, 7th sess., ch. 46/p. 53)
02 Apr 1866
LOS ANGELES lost to creation of KERN. (Calif. Stats. 1865, 16th sess., ch. 569/pp. 796–798)
01 Jan 1873
LOS ANGELES lost to SAN DIEGO. (Political Code 1872, 1: secs. 3944–3945/pp. 140–142)
05 Feb 1877
LOS ANGELES lost to SAN BERNARDINO as a result of an official survey of the boundary. (Coy, 149, 217–219)
Jul 1881
In July 1881, LOS ANGELES lost to VENTURA as a result of an official boundary survey. (Coy, 150–154, 292)
04 Jun 1889
LOS ANGELES lost to creation of ORANGE. Act passed 11 March 1889; referendum for or against creation of new county held 4 June 1889. (Calif. Stats. 1889, 28th sess., ch. 110/pp. 123–129)
23 Jul 1919
The new Political Code authorized LOS ANGELES to exchange with VENTURA. This chapter of the 1919 revision of the laws did not take effect and was found unconstitutional by the California Supreme Court, 19 February 1920. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1919, 43d sess., ch. 470, secs. 3927, 3964/pp. 877–879, 908–909; "Mundell v. Lyons," in Calif. Rpts., 182:289–293; Coy, 152-153)
01 Sep 1987
LOS ANGELES lost small area in Cypress Memorial Park Cemetery to ORANGE. Ordinance passed 29 July 1987; effective 1 September 1987 [change too small to display on interactive map; shapefile users see small_changes 1987_pt. for location]. (Minutes of the Board of Supervisors, Orange County, 29 July 1987, ordinance 3647)
01 Mar 1992
LOS ANGELES lost small area to SAN BERNARDINO. Ordinance passed 27 January 1992; effective 1 March 1992 [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Minutes of the Board of Supervisors, San Bernardino County, 27 January 1992, ordinance 3478)
11 Oct 1993
LOS ANGELES lost small area to SAN BERNARDINO [change too small to display on interactive map; shapefile users see small_changes 1993_pt. for location]. (Calif. Stats. 1993–1994, reg. sess., ch. 1195, sec. 3/p. 6854)
30 Sep 1999
LOS ANGELES lost small area to ORANGE [change too small to display on interactive map; shapefile users see small_changes 1999_pt. for location]. (Minutes of the Board of Supervisors, Los Angeles County, 24 August 1999, ordinance 99–0077M)
19 Sep 2000
Boundary between LOS ANGELES and ORANGE redefined to incorporate 1999 boundary change [no change]. (Calif. Stats. 2000, reg. sess., ch. 506, secs. 15–16 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002)

MADERA

16 May 1893
MADERA created from FRESNO. Act passed 11 March 1893; referendum for or against creation of new county held 16 May 1893. (Calif. Stats. 1893, 30th sess., ch. 143/pp. 168–172; California USGenWeb Project, Madera County, http://www.cagenweb.com/madera/MadHistory.html, 17 July 2002; "Mariposa County v. Madera County," in Calif. Rpts., 142:50–58)

Mare Island

03 May 1852
Mare Island was inadvertently left outside the jurisdiction of any county when SONOMA boundaries were redefined. It remained a non-county area until it became part of SOLANO on 27 January 1853. (Calif. Stats. 1852, 3d sess., ch. 147/p. 236)

MARIN

18 Feb 1850
MARIN created from non-county area; MARIN not fully organized, attached to SONOMA "for judicial purposes." (Calif. Stats. 1849, 1st sess., ch. 15, sec. 11/p. 60)
22 Apr 1850
MARIN fully organized, detached from SONOMA. (Calif. Stats. 1849, 1st sess., ch. 131/p. 406)
25 Apr 1851
MARIN boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 23/pp. 177–178)
15 May 1854
MARIN gained "Island of Los Angeles" (Angel Island) in San Francisco Bay from SAN FRANCISCO. (Calif. Stats. 1854, 5th sess., ch. 67/p. 121)
27 Apr 1855
MARIN lost to SONOMA. (Calif. Stats. 1855, 6th sess., ch. 125/p. 150)
18 Apr 1857
MARIN lost Angel Island in San Francisco Bay to SAN FRANCISCO. (Calif. Stats. 1857, 8th sess., ch. 190/pp. 209–210)
25 Apr 1860
MARIN gained from SONOMA when boundary was changed to run on road [see 13 May 1861]; MARIN gained Angel Island in San Francisco Bay from SAN FRANCISCO. (Calif. Stats. 1860, 11th sess., ch. 288/p. 269)
13 May 1861
MARIN lost to SONOMA [repealed part of act of 25 April 1860]. (Calif. Stats. 1861, 12th sess., ch. 346/p. 351)
26 Mar 1868
MARIN lost the Brothers Islands to CONTRA COSTA. (Calif. Stats. 1867, 17th sess., ch. 305/p. 347)

MARIPOSA

18 Feb 1850
MARIPOSA created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 28/p. 63)
25 Apr 1851
MARIPOSA gained from SAN DIEGO, lost to LOS ANGELES. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 15/pp. 175–176)
20 Apr 1852
MARIPOSA lost to creation of TULARE. (Calif. Stats. 1852, 3d sess., ch. 153/pp. 240–242)
19 Apr 1855
MARIPOSA lost to creation of MERCED. (Calif. Stats. 1855, 6th sess., ch. 104/pp. 125–128)
19 Apr 1856
MARIPOSA lost to creation of FREZNO (now FRESNO). (Calif. Stats. 1856, 7th sess., ch. 127/pp. 183)
24 Apr 1861
MARIPOSA lost a remnant of territory to creation of MONO. (Calif. Stats. 1861, 12th sess., ch. 233/pp. 235–236)
29 Mar 1870
MARIPOSA gained from FRESNO. (Calif. Stats. 1869, 18th sess., ch. 341/p. 449)
01 Apr 1872
MARIPOSA lost to FRESNO. (Calif. Stats. 1871, 19th sess., ch. 602/p. 891)
11 Feb 1874
Boundary between MARIPOSA and FRESNO redefined [no change]. (Calif. Stats. 1873, 20th sess., ch. 88/p. 100)

MENDOCINO

18 Feb 1850
MENDOCINO created from non-county area; MENDOCINO not fully organized, attached to SONOMA "for judicial purposes." (Calif. Stats. 1849, 1st sess., ch. 15, sec. 16/p. 61)
25 Apr 1851
MENDOCINO boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 26/pp. 178–179)
16 Apr 1852
MENDOCINO lost to NAPA. (Calif. Stats. 1852, 3d sess., ch. 116/p. 192)
04 Apr 1855
MENDOCINO lost to NAPA. (Calif. Stats. 1855, 6th sess., ch. 68/p. 77)
27 Apr 1855
MENDOCINO exchanged with SONOMA. (Calif. Stats. 1855, 6th sess., ch. 125/p. 150)
11 Mar 1859
MENDOCINO gained from HUMBOLDT and TRINITY, exchanged with SONOMA. (Calif. Stats. 1859, 10th sess., ch. 108/pp. 98–99)
02 May 1859
MENDOCINO fully organized, detached from SONOMA. (Calif. Stats. 1859, 10th sess., ch. 108, sec. 2/p. 99; History of Mendocino County, 272–273, 283)
28 Apr 1860
MENDOCINO lost to HUMBOLDT and TRINITY. (Calif. Stats. 1860, 11th sess., ch. 340/p. 334)
29 Feb 1864
MENDOCINO lost to LAKE. (Calif. Stats. 1863–1864, 15th sess., ch. 122/p. 111)
30 Oct 1872
MENDOCINO lost to TRINITY when their common boundary was surveyed; later MENDOCINO claimed a different boundary based on an 1891 survey. California Supreme Court upheld 1872 survey on 15 May 1907. (Calif. Stats. 1871, 19th sess., ch. 531/p. 766; "Trinity County v. Mendocino County," in Calif. Rpts., 151: 279–289)
08 Mar 1907
MENDOCINO gained from LAKE, lost to GLENN. (Calif. Stats. 1907, 37th sess., ch. 113/p. 135)
13 Mar 1909
Boundary of LAKE with MENDOCINO and COLUSA redefined [no change]. (Calif. Stats. 1909, 38th sess., ch. 211/pp. 326–328)
30 Jul 1917
MENDOCINO exchanged with SONOMA. (Calif. Stats. 1917, 42d sess., ch. 725/p. 1396)
31 Jul 1917
MENDOCINO exchanged with LAKE. (Calif. Stats. 1917, 42d sess., ch. 779/pp. 1635–1640)

MERCED

19 Apr 1855
MERCED created from MARIPOSA. (Calif. Stats. 1855, 6th sess., ch. 104/pp. 125–128)
19 Apr 1856
MERCED lost to creation of FREZNO (now FRESNO) and lost to TULARE. (Calif. Stats. 1856, 7th sess., ch. 127/pp. 183)
08 Mar 1866
Legislature authorized a re-survey of the MERCED-STANISLAUS line, established in 1854, which would have resulted in MERCED gaining from STANISLAUS. Gain did not take effect; see 13 February 1868. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1865, 16th sess., ch. 191/p. 172; Outcalt, 118–119, 122–123)
13 Feb 1868
Boundary between MERCED and STANISLAUS redefined to confirm 1854 STANISLAUS line; see 8 March 1866 [no change]. (Calif. Stats. 1867, 17th sess., ch. 57/p. 56)
11 Mar 1887
MERCED lost small area to SAN BENITO. (Calif. Stats. 1887, 27th sess., ch. 86/p.103)

MODOC

17 Feb 1874
MODOC created from SISKIYOU. (Calif. Stats. 1873, 20th sess., ch. 107/pp. 124–129)

MONO

24 Apr 1861
MONO created from CALAVERAS, FREZNO (now FRESNO), and remnant of MARIPOSA. Due to uncertainty about the precise location of the boundary between California and Nevada Territory, the county seat of MONO, Aurora, was actually located in Nevada. (Calif. Stats. 1861, 12th sess., ch. 233/pp. 235–236; Chappell, 239–242; "Reddy v. Tinkum," in Calif. Rpts., 60:458–467)
16 Mar 1864
MONO lost to creation of ALPINE. (Calif. Stats. 1863–1864, 15th sess., ch. 180/pp. 178–182)
04 Apr 1864
Legislature authorized creation of COSO from MONO and TULARE; creation did not take effect [see creation of INYO, 22 March 1866]. (Calif. Stats. 1863–1864, 15th sess., ch. 470/pp. 528–530)
02 Mar 1866
MONO gained remnant of AMADOR that was left separate from the rest of AMADOR after the creation of ALPINE. (Calif. Stats. 1865, 16th sess., ch. 161/p. 144)
22 Mar 1866
MONO lost to creation of INYO; INYO boundaries were identical to those of COSO (proposed) [see 4 April 1864]. (Calif. Stats. 1865, 16th sess., ch. 316/pp. 355–358)
22 Jan 1870
MONO gained from TULARE the remnant of territory that was separated from TULARE by the creation of INYO on 22 March 1866. (Calif. Stats. 1869, 18th sess., ch. 18/p. 20)
28 Mar 1870
MONO lost to INYO. (Calif. Stats. 1869, 18th sess., ch. 323/p. 421)

MONTEREY

18 Feb 1850
MONTEREY created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 6/p. 59)
25 Apr 1851
MONTEREY exchanged with SAN LUIS OBISPO. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 6/p. 173)
13 May 1861
MONTEREY lost to SAN LUIS OBISPO. (Calif. Stats. 1861, 12th sess., ch. 342/p. 349)
20 Apr 1863
MONTEREY gained from SAN LUIS OBISPO. (Calif. Stats. 1863, 14th sess., ch. 276/p. 358)
12 Feb 1874
MONTEREY lost to creation of SAN BENITO. (Calif. Stats. 1873, 20th sess., ch. 87/pp. 95–99)

NAPA

18 Feb 1850
NAPA created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 15/p. 61)
25 Apr 1851
NAPA boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 25/p. 178)
16 Apr 1852
NAPA gained from MENDOCINO. (Calif. Stats. 1852, 3d sess., ch. 116/p. 192)
04 Apr 1855
NAPA gained from MENDOCINO, SOLANO, and SONOMA. (Calif. Stats. 1855, 6th sess., ch. 68/p. 77)
20 May 1861
NAPA lost to creation of LAKE. (Calif. Stats. 1861, 12th sess., ch. 498/pp. 560–561)
29 Feb 1864
NAPA lost to LAKE. (Calif. Stats. 1863–1864, 15th sess., ch. 122/p. 111)
24 Mar 1868
NAPA lost small area to LAKE. (Calif. Stats. 1867, 17th sess., ch. 257/p. 269)
08 Mar 1872
NAPA gained from LAKE. (Calif. Stats. 1871, 19th sess., ch. 229/p. 305)

NEVADA

25 Apr 1851
NEVADA created from YUBA. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 20/p. 177)
03 May 1852
NEVADA gained from SIERRA. (Calif. Stats. 1852, 3d sess., chs. 114–115/pp. 190–192)
19 Apr 1856
NEVADA gained from SIERRA. (Calif. Stats. 1856, 7th sess., ch. 122/p. 143)
28 Dec 1908
California Supreme Court settled boundary dispute between NEVADA and SIERRA in favor of SIERRA. Dispute grew out of disagreement over the location of the source of the South Fork of Middle Yuba River [no change]. ("Sierra County v. Nevada County," in Calif. Rpts., 155:1–15)
01 Mar 1909
NEVADA boundary with SIERRA clarified to run on public land survey lines [no discernible change]. (Calif. Stats. 1909, 38th sess., ch. 75, sec. 2/p. 86)

ORANGE

04 Jun 1889
ORANGE created from LOS ANGELES. Act passed 11 March 1889; referendum for or against creation of new county held 4 June 1889. (Calif. Stats. 1889, 28th sess., ch. 110/pp. 123–129)
01 Sep 1987
ORANGE gained small area in Cypress Memorial Park Cemetery from LOS ANGELES. Ordinance passed 29 July 1987; effective 1 September 1987 [change too small to display on interactive map; shapefile users see small_changes 1987_pt. for location]. (Minutes of the Board of Supervisors, Orange County, 29 July 1987, ordinance 3647)
08 Nov 1988
ORANGE exchanged small areas with RIVERSIDE. Ordinance passed 27 September 1988; effective 8 November 1988. (Minutes of the Board of Supervisors, Riverside County, 27 September 1988, ordinance 665)
01 Jul 1992
Boundary between ORANGE and RIVERSIDE restated [no change]. Ordinance passed 26 November 1991; effective 1 July 1992. (Minutes of the Board of Supervisors, Riverside County, 26 November 1991, ordinance 717)
11 Oct 1993
ORANGE boundaries redefined [no change]. (Calif. Stats. 1993–1994, reg. sess., ch. 1195, sec. 4/pp. 6855–6858)
30 Sep 1999
ORANGE gained small area from LOS ANGELES [change too small to display on interactive map; shapefile users see small_changes 1999_pt. for location]. (Minutes of the Board of Supervisors, Los Angeles County, 24 August 1999, ordinance 99–0077M)
19 Sep 2000
Boundary between ORANGE and LOS ANGELES redefined to incorporate 1999 boundary change [no change]. (Calif. Stats. 2000, reg. sess., ch. 506, secs. 15–16 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002)

PAUTAH (proposed)

03 May 1852
California Legislature proposed creation of PAUTAH in Utah Territory (present Nevada). Creation never took effect because the United States never ceded the area to California. (Calif. Stats. 1852, 3d sess., ch. 118/p. 193; "Historical and Political Data, Carson County, Utah Territory," Political History of Nevada 1996, http://dmla.clan.lib.nv.us/docs/nsla/archives/political/historical/hist05.htm, 12 December 2002)
08 Apr 1859
PAUTAH legally eliminated; ended the attempt by California to gain part of Utah Territory (present Nevada). (Calif. Stats. 1859, 10th sess., ch. 183/p. 186)

PLACER

25 Apr 1851
PLACER created from SUTTER and YUBA. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 17/p. 176)
20 Apr 1863
PLACER lost to EL DORADO. (Calif. Stats. 1863, 14th sess., ch. 263/p. 349)
13 Mar 1866
PLACER exchanged with SUTTER. (Calif. Stats. 1865, 16th sess., ch. 224/p. 223)
01 Jan 1873
PLACER gained small area from SUTTER. (Political Code 1872, 1: sec. 3924, 3926/pp. 125–127)
19 Mar 1889
PLACER boundaries clarified [no change]. (Calif. Stats. 1889, 28th sess., ch. 262/p. 402)
10 Aug 1913
PLACER exchanged with EL DORADO. (Calif. Stats. 1913, 40th sess., chs. 315–316/pp. 603–605)

PLUMAS

01 Apr 1854
PLUMAS created from BUTTE. (Calif. Stats. 1854, 5th sess., ch. 1/pp. 129–131)
27 Mar 1863
PLUMAS lost to SIERRA. (Calif. Stats. 1863, 14th sess., ch. 101/p. 114; Sinnott, 6:19–22)
01 Apr 1864
PLUMAS lost to creation of LASSEN. (Calif. Stats. 1863–1864, 15th sess., ch. 261/pp. 264–269)
31 Mar 1866
PLUMAS gained from SIERRA and gained small area from YUBA. (Calif. Stats. 1865, 16th sess., ch. 466/p. 605)
28 Mar 1868
PLUMAS lost small area to SIERRA. (Calif. Stats. 1867, 17th sess., ch. 377/p. 462)
01 Jan 1873
PLUMAS lost to LASSEN and SHASTA. (Political Code 1872, 1: secs. 3911–3912, 3920/pp. 115–116, 122–123)
16 Mar 1874
PLUMAS lost small area to SIERRA when boundary was set on public land survey lines. (Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, p. 166)
28 Feb 1901
PLUMAS exchanged with LASSEN. (Calif. Stats. 1901, 34th sess., ch. 61/pp. 76–80)
23 Mar 1901
PLUMAS exchanged with BUTTE; boundary between PLUMAS and SHASTA clarified to run on public land survey line [no discernible change]. (Calif. Stats. 1901, 34th sess., chs. 146, 171/pp. 549–551, 560)

RIVERSIDE

02 May 1893
RIVERSIDE created from SAN BERNARDINO and SAN DIEGO. Act passed 11 March 1893; referendum for or against creation of new county held 2 May 1893. (Calif. Stats. 1893, 30th sess., ch. 142/pp. 158–168)
22 Jul 1919
RIVERSIDE exchanged with SAN BERNARDINO. (Calif. Stats. 1919, 43d sess., ch. 62/p. 99)
16 Jun 1967
RIVERSIDE boundaries redefined to more precisely define the boundary between RIVERSIDE and the State of Arizona [no discernible change]. (Calif. Stats. 1967, reg. sess., ch. 340/pp. 1537–1539; Coy, 340)
08 Nov 1988
RIVERSIDE exchanged small areas with ORANGE. Ordinance passed 27 September 1988; effective 8 November 1988. (Minutes of the Board of Supervisors, Riverside County, 27 September 1988, ordinance 665)
01 Jul 1992
Boundary between RIVERSIDE and ORANGE restated [no change]. Ordinance passed 26 November 1991; effective 1 July 1992. (Minutes of the Board of Supervisors, Riverside County, 26 November 1991, ordinance 717)
11 Oct 1993
RIVERSIDE boundaries redefined [no change]. (Calif. Stats. 1993–1994, reg. sess., ch. 1195, sec. 5/pp. 6858–6860)

SACRAMENTO

18 Feb 1850
SACRAMENTO created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 17/p. 61; Tinkham, 64)
25 Apr 1851
SACRAMENTO boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 11/p. 174)
30 Mar 1857
SACRAMENTO boundaries redefined [no change]. (Calif. Stats. 1857, 8th sess., ch. 120/p. 132)
23 Apr 1861
SACRAMENTO gained from SAN JOAQUIN. (Calif. Stats. 1861, 12th sess., ch. 219/p. 221; Tinkham, 64–65)
13 Mar 1866
SACRAMENTO boundaries redefined [no change]. (Calif. Stats. 1865, 16th sess., ch. 224/p. 223)
12 Mar 1870
SACRAMENTO gained small areas from SOLANO and YOLO. (Calif. Stats. 1869, 18th sess., ch. 191/p. 294)
01 Apr 1878
SACRAMENTO lost to SAN JOAQUIN. (Calif. Stats. 1877, 22d sess., Acts Amendatory of the Political Code, ch. 636/p. 70)
18 Mar 1905
Boundary between SACRAMENTO and SAN JOAQUIN redefined [no change]. (Calif. Stats. 1905, 36th sess., ch. 167/p. 164)
14 Jul 1988
SACRAMENTO boundaries redefined [no change]. (Calif. Stats. 1987–1988, reg. sess., ch. 363/p. 1676)

SAN BENITO

12 Feb 1874
SAN BENITO created from MONTEREY. (Calif. Stats. 1873, 20th sess., ch. 87/pp. 95–99)
11 Mar 1887
SAN BENITO gained from FRESNO and gained small area from MERCED. (Calif. Stats. 1887, 27th sess., ch. 86/p.103)

SAN BERNARDINO

26 Apr 1853
SAN BERNARDINO created from LOS ANGELES. (Calif. Stats. 1853, 4th sess., ch. 78/pp. 119–123)
02 Apr 1857
SAN BERNARDINO boundaries redefined [no change]. (Calif. Stats. 1857, 8th sess., ch. 142/p. 165)
01 Jan 1873
SAN BERNARDINO gained from SAN DIEGO, lost to INYO. (Political Code 1872, 1: secs. 3942–3944/pp. 139–141)
05 Feb 1877
SAN BERNARDINO gained from LOS ANGELES as a result of an official survey of the boundary. (Coy, 149, 217–219)
02 May 1893
SAN BERNARDINO lost to creation of RIVERSIDE. Act passed 11 March 1893; referendum for or against creation of new county held 2 May 1893. (Calif. Stats. 1893, 30th sess., ch. 142/pp. 158–168)
27 Jul 1917
SAN BERNARDINO gained from KERN. (Calif. Stats. 1917, 42d sess., ch. 205/p. 301)
22 Jul 1919
SAN BERNARDINO exchanged with RIVERSIDE. (Calif. Stats. 1919, 43d sess., ch. 62/p. 99)
19 Sep 1947
Boundary between SAN BERNARDINO and INYO placed in dispute. Section 23136 of Political Code was revised to authorize SAN BERNARDINO to gain from INYO a strip of territory one and one-half miles wide between the San Bernardino Meridian and the state line. The companion description of INYO boundaries in section 23114 authorized no such change [no change]. (Calif. Stats. 1947, reg. sess., ch. 424, secs. 23114, 23136/pp. 1050, 1068)
11 Sep 1957
SAN BERNARDINO gained small area from INYO; boundaries of SAN BERNARDINO and INYO clarified, ending boundary dispute dating from 1947. (Calif. Stats. 1957, reg. sess., ch. 2382/p. 4119)
13 May 1963
SAN BERNARDINO exchanged small areas with KERN. (Coy, 340, 342; correspondence, California Board of Equalization, 25 July 2002)
11 Jul 1967
SAN BERNARDINO boundaries redefined to more precisely define the boundary between SAN BERNARDINO and the State of Arizona [exchange of territory too small to map]. (Calif. Stats. 1967, reg. sess., ch. 655/pp. 2024–2026; Coy, 341–342)
1972
In 1972, boundary between INYO and SAN BERNARDINO was adjusted [precise location unknown, not mapped]. (Correspondence, California State Board of Equalization, 25 July 2002)
01 Mar 1992
SAN BERNARDINO gained small area from LOS ANGELES. Ordinance passed 27 January 1992; effective 1 March 1992 [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Minutes of the Board of Supervisors, San Bernardino County, 27 January 1992, ordinance 3478)
11 Oct 1993
SAN BERNARDINO gained small area from LOS ANGELES [change too small to display on interactive map; shapefile users see small_changes 1993_pt. for location]. (Calif. Stats. 1993–1994, reg. sess., ch. 1195, sec. 3/p. 6854)

SAN DIEGO

18 Feb 1850
SAN DIEGO created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 2/pp. 58–59)
25 Apr 1851
SAN DIEGO exchanged with LOS ANGELES, lost to MARIPOSA. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 2/p. 172)
30 Mar 1868
SAN DIEGO boundaries clarified [no change]. (Calif. Stats. 1867, 17th sess., ch. 453/p. 604)
01 Jan 1873
SAN DIEGO gained from LOS ANGELES, lost to SAN BERNARDINO. (Political Code 1872, 1: secs. 3943–3945/pp. 140–142)
02 May 1893
SAN DIEGO lost to creation of RIVERSIDE. Act passed 11 March 1893; referendum for or against creation of new county held 2 May 1893. (Calif. Stats. 1893, 30th sess., ch. 142/pp. 158–168)
12 Aug 1907
SAN DIEGO lost to creation of IMPERIAL. (Coy, 50–51; Farr, 18–19)

SAN FRANCISCO

18 Feb 1850
SAN FRANCISCO created from non-county area; southern boundary with BRANCIFORTE (now SANTA CRUZ) was in dispute when the counties disagreed over the interpretation of the boundary description. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 8/pp. 59–60; Stanger, 88)
05 Apr 1850
SAN FRANCISCO boundaries in San Francisco Bay clarified [no change]. (Calif. Stats. 1849, 1st sess., ch. 61, sec. 2/p. 156)
25 Apr 1851
SAN FRANCISCO boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 8/p. 174)
15 May 1854
SAN FRANCISCO lost "Island of Los Angeles" (Angel Island) in San Francisco Bay to MARIN. (Calif. Stats. 1854, 5th sess., ch. 67/p. 121)
01 Jul 1856
SAN FRANCISCO lost to creation of SAN MATEO. Act passed 19 April 1856; took effect 1 July 1856. (Calif. Stats. 1856, 7th sess., ch. 125/pp. 145–146, 176–178)
18 Apr 1857
SAN FRANCISCO gained Angel Island in San Francisco Bay from MARIN. Boundary between SAN FRANCISCO and SAN MATEO adjusted to run on public land survey line [no discernible change]. (Calif. Stats. 1857, 8th sess., chs. 190, 192/pp. 209–210, 222–223)
25 Apr 1860
SAN FRANCISCO lost Angel Island in San Francisco Bay to MARIN. (Calif. Stats. 1860, 11th sess., ch. 288/p. 269)
30 Mar 1874
SAN FRANCISCO lost small area in San Francisco Bay to ALAMEDA; placed all of the Central Pacific Railroad Wharf in ALAMEDA. The wharf was removed in 1919 [change too small to display on interactive map; shapefile users see small_changes 1874_pt. for location]. (Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, pp. 168–170; Coy, 62–63)
1949–1959
Between 1949 and 1959 (precise date unknown), SAN FRANCISCO gained a small area of the Alameda Naval Air Station when landfill expansion extended westward over the county line between SAN FRANCISCO and ALAMEDA in San Francisco Bay. (U.S.G.S., 7.5 Minute Series, Oakland West Quadrangle, "Edition of 1949" and "Edition of 1959")

SAN JOAQUIN

18 Feb 1850
SAN JOAQUIN created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 26/p. 63; Tinkham, 64)
25 Apr 1851
SAN JOAQUIN boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 12/p. 175)
14 Feb 1852
SAN JOAQUIN gained from CONTRA COSTA. (Calif. Stats. 1852, 3d sess., chs. 105–106/pp. 178–180; Purcell, 250)
17 Feb 1860
SAN JOAQUIN lost to STANISLAUS. (Calif. Stats. 1860, 11th sess., ch. 62/pp. 34–35)
23 Apr 1861
SAN JOAQUIN lost to SACRAMENTO. (Calif. Stats. 1861, 12th sess., ch. 219/p. 221; Tinkham, 64–65)
01 Apr 1878
SAN JOAQUIN gained from SACRAMENTO. (Calif. Stats. 1877, 22d sess., Acts Amendatory of the Political Code, ch. 636/p. 70)
18 Mar 1905
Boundary between SAN JOAQUIN and SACRAMENTO redefined [no change]. (Calif. Stats. 1905, 36th sess., ch. 167/p. 164)

SAN LUIS OBISPO

18 Feb 1850
SAN LUIS OBISPO created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 5/p. 59)
25 Apr 1851
SAN LUIS OBISPO gained from SANTA BARBARA, exchanged with MONTEREY. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 5/p. 173)
24 Apr 1852
SAN LUIS OBISPO lost to SANTA BARBARA. (Calif. Stats. 1852, 3d sess., ch. 133/p. 218)
13 May 1854
SAN LUIS OBISPO exchanged with SANTA BARBARA. (Calif. Stats. 1854, 5th sess., ch. 24/p. 148)
13 May 1861
SAN LUIS OBISPO gained from MONTEREY. (Calif. Stats. 1861, 12th sess., ch. 342/p. 349)
20 Apr 1863
SAN LUIS OBISPO lost to MONTEREY. (Calif. Stats. 1863, 14th sess., ch. 276/p. 358)
01 Jan 1873
SAN LUIS OBISPO exchanged with SANTA BARBARA, lost to creation of VENTURA. (Calif. Stats. 1871, 19th sess., ch. 351/pp. 484–489; Political Code 1872, 1: secs. 3946–3947/pp. 142–143)
14 Mar 1885
SAN LUIS OBISPO exchanged with KERN. (Calif. Stats. 1885, 26th sess., ch. 149/pp. 139–141)
02 May 1991
SAN LUIS OBISPO lost small area to SANTA BARBARA [change too small to display on interactive map; shapefile users see small_changes 1991_pt. for location]. (Leaha K. Magee, San Luis Obispo County LAFCO, correspondence, 29 October 2002)
09 Jul 1992
SAN LUIS OBISPO lost small area to SANTA BARBARA [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Leaha K. Magee, San Luis Obispo County LAFCO, correspondence, 29 October 2002)

SAN MATEO

01 Jul 1856
SAN MATEO created from SAN FRANCISCO; southern boundary with SANTA CRUZ was in dispute [see 18 February 1850]. Act passed 19 April 1856; took effect 1 July 1856. (Calif. Stats. 1856, 7th sess., ch. 125/pp. 145–146, 176–178)
18 Apr 1857
Boundary between SAN FRANCISCO and SAN MATEO adjusted to run on public land survey line [no discernible change]. SAN MATEO boundaries clarified, ending dispute with SANTA CRUZ; gave SAN MATEO control over area disputed with SANTA CRUZ. (Calif. Stats. 1857, 8th sess., chs. 190, 192/pp. 209–210, 222–223; Stanger, 88)
16 Mar 1868
SAN MATEO gained from SANTA CRUZ. (Calif. Stats. 1867, 17th sess., ch. 195/p. 174)
14 Mar 1878
Boundary between SAN MATEO and ALAMEDA in San Francisco Bay was adjusted [not mapped]. (Calif. Stats. 1877, 22d sess., Acts Amendatory of the Political Code, ch. 197/p. 71)
14 Mar 1901
SAN MATEO boundaries clarified [no change]. (Calif. Stats. 1901, 34th sess., ch. 128/p. 291)
14 Oct 1963
SAN MATEO lost small area to SANTA CLARA [change too small to display on interactive map; shapefile users see small_changes 1963_pt. for location]. (Coy, 342–343, 345)
11 Jul 1968
SAN MATEO boundaries clarified [no change]. (Calif. Stats. 1968, reg. sess., ch. 537, sec. 1/pp. 1189–1191)

SANTA BARBARA

18 Feb 1850
SANTA BARBARA created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 4/p. 59)
25 Apr 1851
SANTA BARBARA exchanged with LOS ANGELES, lost to SAN LUIS OBISPO. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 4/p. 173)
24 Apr 1852
SANTA BARBARA gained from SAN LUIS OBISPO. (Calif. Stats. 1852, 3d sess., ch. 133/p. 218)
13 May 1854
SANTA BARBARA exchanged with SAN LUIS OBISPO. (Calif. Stats. 1854, 5th sess., ch. 24/p. 148)
01 Jan 1873
SANTA BARBARA exchanged with SAN LUIS OBISPO, lost to creation of VENTURA. (Calif. Stats. 1871, 19th sess., ch. 351/pp. 484–489; Political Code 1872, 1: secs. 3946–3947/pp. 142–143)
05 Jun 1968
SANTA BARBARA boundaries redefined to correct mistake in Government Political Code. The word "northwest" was replaced by "southwestern" [no change]. (Calif. Stats. 1968, reg. sess., ch. 248/p. 561)
02 May 1991
SANTA BARBARA gained small area from SAN LUIS OBISPO [change too small to display on interactive map; shapefile users see small_changes 1991_pt. for location]. (Leaha K. Magee, San Luis Obispo County LAFCO, correspondence, 29 October 2002)
09 Jul 1992
SANTA BARBARA gained small area from SAN LUIS OBISPO [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Leaha K. Magee, San Luis Obispo County LAFCO, correspondence, 29 October 2002)

SANTA CLARA

18 Feb 1850
SANTA CLARA created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 9/p. 60)
05 Apr 1850
SANTA CLARA boundaries clarified [no change]. (Calif. Stats. 1849, 1st sess., ch. 61, sec. 3/p. 156)
25 Apr 1851
SANTA CLARA boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 9/p. 174)
25 Mar 1853
SANTA CLARA gained small remnant from CONTRA COSTA, lost to creation of ALAMEDA. (Calif. Stats. 1853, 4th sess., ch. 41/pp. 56–59)
14 Oct 1963
SANTA CLARA gained small area from SAN MATEO [change too small to display on interactive map; shapefile users see small_changes 1963_pt. for location]. (Coy, 342–343, 345)
11 Jul 1968
SANTA CLARA boundaries clarified [no change]. (Calif. Stats. 1968, reg. sess., ch. 537, sec. 2/pp. 1191–1193)
02 Nov 1971
SANTA CLARA gained small areas from ALAMEDA [change too small to display on interactive map; shapefile users see small_changes 1971_pt. for location]. (Coy, 338, 343)
17 Nov 1971
SANTA CLARA exchanged small areas with SANTA CRUZ as the boundary was clarified along its entire length [not mapped]. (Coy, 343–345)
07 Apr 1976
SANTA CLARA boundaries clarified [no change]. (Calif. Stats. 1976, reg. sess., ch. 102, sec. 1/pp. 161–162)
11 Dec 1998
SANTA CLARA gained small area from SANTA CRUZ [precise location unknown, not mapped]. (Correspondence, California State Board of Equalization, 25 July 2002)

SANTA CRUZ

18 Feb 1850
BRANCIFORTE (now SANTA CRUZ) created from non-county area; northern boundary with SAN FRANCISCO was in dispute when the counties disagreed over the interpretation of the boundary description. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 7/p. 59; Stanger, 88)
05 Apr 1850
BRANCIFORTE renamed SANTA CRUZ; boundaries redefined [no change]. (Calif. Stats. 1849, 1st sess., ch. 61, sec. 1/pp. 155–156)
25 Apr 1851
SANTA CRUZ boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 7/p. 173)
01 Jul 1856
SAN MATEO created from SAN FRANCISCO; SAN MATEO boundary with SANTA CRUZ was in dispute [see 18 February 1850]. (Calif. Stats. 1856, 7th sess., ch. 125/pp. 145–146, 176–178)
18 Apr 1857
SAN MATEO boundaries clarified, ending dispute with SANTA CRUZ; SANTA CRUZ lost control of area disputed with SAN MATEO. (Calif. Stats. 1857, 8th sess., ch. 192/pp. 222–223; Stanger, 88)
16 Mar 1868
SANTA CRUZ lost to SAN MATEO. (Calif. Stats. 1867, 17th sess., ch. 195/p. 174)
17 Nov 1971
SANTA CRUZ exchanged small areas with SANTA CLARA as the boundary was clarified along its entire length [not mapped]. (Coy, 343–345)
07 Apr 1976
SANTA CRUZ boundaries clarified [no change]. (Calif. Stats. 1976, reg. sess., ch. 102, sec. 2/pp. 162–165)
11 Dec 1998
SANTA CRUZ lost small area to SANTA CLARA [precise location unknown, not mapped]. (Correspondence, California State Board of Equalization, 25 July 2002)

SHASTA

18 Feb 1850
SHASTA created from non-county area. TRINITY not fully organized, attached to SHASTA for judicial and other purposes. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 23/p. 62)
25 Apr 1851
SHASTA gained from COLUSI (now COLUSA), and gained small area from BUTTE. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 22/p. 177)
09 Jun 1851
TRINITY fully organized; detached from SHASTA. (Calif. Stats. 1851, 2d sess., ch. 132/pp. 516–518; Cox, 116–117)
22 Mar 1852
SHASTA lost to creation of SISKIYOU. (Calif. Stats. 1852, 3d sess., ch. 146/pp. 233–235)
24 Apr 1852
SHASTA boundaries redefined [no change]. (Calif. Stats. 1852, 3d sess., ch. 142/p. 228)
09 Apr 1856
SHASTA lost to creation of TEHAMA. (Calif. Stats. 1856, 7th sess., ch. 100/pp. 118–119)
21 Apr 1856
SHASTA exchanged with TEHAMA. (Calif. Stats. 1856, 7th sess., ch. 141/p. 222)
19 Feb 1857
SHASTA exchanged with TEHAMA. (Calif. Stats. 1857, 8th sess., ch. 37/p. 25)
01 Apr 1864
SHASTA lost to creation of LASSEN. (Calif. Stats. 1863–1864, 15th sess., ch. 261/pp. 264–269)
01 Jan 1873
SHASTA gained from PLUMAS. (Political Code 1872, 1: secs. 3911, 3915, 3920/pp. 115, 118, 122–123)
14 Mar 1899
SHASTA lost to LASSEN. (Calif. Stats. 1899, 33d sess., ch. 82/p. 98)
23 Mar 1901
Boundary between SHASTA and PLUMAS clarified to run on public land survey line [no discernible change]. (Calif. Stats. 1901, 34th sess., ch. 171/p. 560)

SIERRA

16 Apr 1852
SIERRA created from YUBA. (Calif. Stats. 1852, 3d sess., ch. 145/pp. 230–231)
03 May 1852
SIERRA lost to NEVADA. (Calif. Stats. 1852, 3d sess., chs. 114–115/pp. 190–192)
19 Apr 1856
SIERRA lost to NEVADA. (Calif. Stats. 1856, 7th sess., ch. 122/p. 143)
27 Mar 1863
SIERRA gained from PLUMAS. (Calif. Stats. 1863, 14th sess., ch. 101/p. 114; Sinnott, 6:19–22)
13 Mar 1866
SIERRA gained from YUBA. (Calif. Stats. 1865, 16th sess., ch. 229/p. 228)
31 Mar 1866
SIERRA lost to PLUMAS. (Calif. Stats. 1865, 16th sess., ch. 466/p. 605)
28 Mar 1868
SIERRA gained small area from PLUMAS. (Calif. Stats. 1867, 17th sess., ch. 377/p. 462)
16 Mar 1874
SIERRA gained from LASSEN and PLUMAS when boundary was set on public land survey lines. (Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, p. 166)
28 Dec 1908
California Supreme Court settled boundary dispute between SIERRA and NEVADA in favor of SIERRA. Dispute grew out of disagreement over the location of the source of the South Fork of Middle Yuba River [no change]. ("Sierra County v. Nevada County," in Calif. Rpts., 155:1–15)
01 Mar 1909
SIERRA boundaries clarified [no change]. (Calif. Stats. 1909, 38th sess., ch. 75, sec. 1/p. 86)

SISKIYOU

22 Mar 1852
SISKIYOU created from KLAMATH (extinct) and SHASTA. (Calif. Stats. 1852, 3d sess., ch. 146/pp. 233–235)
02 Mar 1857
SISKIYOU lost small area to creation of DEL NORTE. (Calif. Stats. 1857, 8th sess., ch. 52/pp. 35–36)
01 Jan 1873
SISKIYOU exchanged with DEL NORTE. (Political Code 1872, 1:secs. 3909, 3913/pp. 113–114, 117)
17 Feb 1874
SISKIYOU lost to creation of MODOC. (Calif. Stats. 1873, 20th sess., ch. 107/pp. 124–129)
30 May 1874
SISKIYOU gained part of KLAMATH; KLAMATH eliminated. Act passed 28 March 1874; referendum for annexation of KLAMATH held 30 May 1874. (Calif. Stats. 1873, 20th sess., ch. 520/pp. 755–758; Kasch, 270–272)
11 Mar 1887
SISKIYOU exchanged with DEL NORTE. (Calif. Stats. 1887, 27th sess., ch. 88/pp. 105–107)
23 Mar 1901
SISKIYOU gained small area from HUMBOLDT. (Calif. Stats. 1901, 34th sess., ch. 193/p. 600)

SOLANO

18 Feb 1850
SOLANO created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 13/p. 61)
25 Apr 1851
SOLANO boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 27/p. 179)
27 Jan 1853
SOLANO gained Mare Island, a non-county area that had been part of SONOMA until 3 May 1852. (Calif. Stats. 1853, 4th sess., ch. 5/p. 20)
04 Apr 1855
SOLANO lost to NAPA. (Calif. Stats. 1855, 6th sess., ch. 68/p. 77)
27 Apr 1855
SOLANO gained from SONOMA. (Calif. Stats. 1855, 6th sess., ch. 125/p. 150)
26 Mar 1857
SOLANO lost to YOLO. (Calif. Stats. 1857, 8th sess., ch. 104/p. 108)
12 Mar 1870
SOLANO lost small area to SACRAMENTO. (Calif. Stats. 1869, 18th sess., ch. 191/p. 294)
01 Jan 1980
SOLANO lost small area to YOLO. Ordinance passed 20 November 1979; effective 1 January 1980 [change too small to display on interactive map; shapefile users see small_changes 1980_pt. for location]. (Minutes of the Board of Supervisors, Solano County, 20 November 1979, ordinance 1085; Minutes of the Board of Supervisors, Yolo County, 20 November 1979, ordinance 861)
18 Dec 1992
SOLANO lost small area to YOLO [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Minutes of the Board of Supervisors, Solano County, 8 December 1992, ordinance 1460; Minutes of the Board of Supervisors, Yolo County, 24 November 1992, ordinance 1153)

SONOMA

18 Feb 1850
SONOMA created from non-county area. MARIN and MENDOCINO not fully organized, attached to SONOMA "for judicial purposes." (Calif. Stats. 1849, 1st sess., ch. 15, sec. 12/p. 60)
22 Apr 1850
MARIN fully organized, detached from SONOMA. MENDOCINO remained attached to SONOMA. (Calif. Stats. 1849, 1st sess., ch. 131/p. 406)
25 Apr 1851
SONOMA boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 24/p. 178)
03 May 1852
SONOMA lost Mare Island when SONOMA boundaries were redefined. Mare Island remained a non-county area until 27 January 1853 when it became part of SOLANO. (Calif. Stats. 1852, 3d sess., ch. 147/p. 236)
04 Apr 1855
SONOMA lost to NAPA. (Calif. Stats. 1855, 6th sess., ch. 68/p. 77)
27 Apr 1855
SONOMA gained from MARIN, exchanged with MENDOCINO, lost to SOLANO. (Calif. Stats. 1855, 6th sess., ch. 125/p. 150)
11 Mar 1859
SONOMA exchanged with MENDOCINO. (Calif. Stats. 1859, 10th sess., ch. 108/pp. 98–99)
02 May 1859
MENDOCINO fully organized, detached from SONOMA. (Calif. Stats. 1859, 10th sess., ch. 108, sec. 2/p. 99; History of Mendocino County, 272–273, 283)
25 Apr 1860
SONOMA lost to MARIN when boundary was changed to run on road [see 13 May 1861]. (Calif. Stats. 1860, 11th sess., ch. 288/p. 269)
13 May 1861
SONOMA gained from MARIN [repealed part of act of 25 April 1860]. (Calif. Stats. 1861, 12th sess., ch. 346/p. 351)
10 Feb 1868
SONOMA boundaries redefined [no change]. (Calif. Stats. 1867, 17th sess., ch. 45/p. 42)
30 Jul 1917
SONOMA exchanged with MENDOCINO. (Calif. Stats. 1917, 42d sess., ch. 725/p. 1396)

STANISLAUS

05 Apr 1854
STANISLAUS created from TUOLUMNE. (Calif. Stats. 1854, 5th sess., chs. 35, 81/pp. 40–41, 191–194)
04 May 1855
Boundary between STANISLAUS and TUOLUMNE clarified [no change]. (Calif. Stats. 1855, 6th sess., ch. 194/p. 245)
17 Feb 1860
STANISLAUS gained from SAN JOAQUIN. (Calif. Stats. 1860, 11th sess., ch. 62/pp. 34–35)
08 Mar 1866
Legislature authorized a re-survey of the STANISLAUS-MERCED line, established in 1854, which would have resulted in STANISLAUS losing to MERCED. Loss did not take effect; see 13 February 1868. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1865, 16th sess., ch. 191/p. 172; Outcalt, 118–119, 122–123)
13 Feb 1868
Boundary between STANISLAUS and MERCED redefined to confirm 1854 STANISLAUS line; see 8 March 1866 [no change]. (Calif. Stats. 1867, 17th sess., ch. 57/p. 56)
02 Jul 1986
STANISLAUS boundaries clarified [no change]. (Calif. Stats. 1985–1986, reg. sess., ch. 248, sec. 80/p. 1239)

SUTTER

18 Feb 1850
SUTTER created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 19/p. 62)
25 Apr 1851
SUTTER gained from YUBA, lost to BUTTE, and lost to creation of PLACER. (Calif. Stats. 1851, 2d sess., ch. 14, secs. 17–18/p. 176)
03 May 1852
SUTTER exchanged with BUTTE. (Calif. Stats. 1852, 3d sess., ch. 149/p. 237)
31 Mar 1854
SUTTER gained from BUTTE. (Calif. Stats. 1854, 5th sess., ch. 16/p. 26)
19 Apr 1856
SUTTER lost to COLUSI (now COLUSA). (Calif. Stats. 1856, 7th sess., ch. 105/p. 124)
21 Apr 1856
SUTTER gained from BUTTE. (Calif. Stats. 1856, 7th sess., ch. 150/p. 231)
01 Apr 1864
SUTTER gained from BUTTE. (Calif. Stats. 1863–1864, 15th sess., ch. 292/p. 301)
13 Mar 1866
SUTTER exchanged with PLACER. (Calif. Stats. 1865, 16th sess., ch. 224/p. 223)
01 Jan 1873
SUTTER lost small area to PLACER. (Political Code 1872, 1: secs. 3924, 3926/pp. 125–127)
31 Mar 1891
SUTTER gained small area from COLUSA [change too small to display on interactive map; shapefile users see small_changes 1891_pt. for location]. (Calif. Stats. 1891, 29th sess., ch. 240/p. 455)
09 Sep 1953
SUTTER exchanged with YUBA along Bear River. (Calif. Stats. 1953, reg. sess., ch. 836, sec. 1/pp. 2148–2152)
28 Mar 1994
SUTTER lost small area to YUBA [change too small to display on interactive map; shapefile users see small_changes 1994_pt. for location]. (Minutes of the Board of Supervisors, Yuba County, 20 July 1993, ordinance 1140)

TEHAMA

09 Apr 1856
TEHAMA created from BUTTE, COLUSI (now COLUSA), and SHASTA. (Calif. Stats. 1856, 7th sess., ch. 100/pp. 118–119)
21 Apr 1856
TEHAMA exchanged with SHASTA. (Calif. Stats. 1856, 7th sess., ch. 141/p. 222)
19 Feb 1857
TEHAMA exchanged with SHASTA, lost to COLUSI (now COLUSA). (Calif. Stats. 1857, 8th sess., ch. 37/p. 25)
26 Mar 1857
TEHAMA boundaries redefined [no change]. (Calif. Stats. 1857, 8th sess., ch. 105/p. 109)
19 Apr 1859
TEHAMA gained from COLUSA, lost to BUTTE. (Calif. Stats. 1859, 10th sess., ch. 322/p. 359)
01 Jan 1873
TEHAMA lost to COLUSA. (Political Code 1872, 1: secs. 3915–3916/pp. 118–119)
20 Nov 1944
TEHAMA exchanged with BUTTE. (Coy, 339, 345)

TRINITY

18 Feb 1850
TRINITY created from non-county area; TRINITY not fully organized, attached to SHASTA for judicial and other purposes. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 24/p. 62)
25 Apr 1851
TRINITY lost to creation of KLAMATH (extinct). (Calif. Stats. 1851, 2d sess., ch. 14, secs. 30–31/pp. 179–180)
09 Jun 1851
TRINITY fully organized; detached from SHASTA. (Calif. Stats. 1851, 2d sess., ch. 132/pp. 516–518; Cox, 116–117)
12 May 1853
TRINITY lost to creation of HUMBOLDT. (Calif. Stats. 1853, 4th sess., ch. 114/pp. 161–164)
30 Apr 1855
TRINITY gained from KLAMATH (extinct). (Calif. Stats. 1855, 6th sess., ch. 156/p. 200)
11 Mar 1859
TRINITY lost to MENDOCINO. (Calif. Stats. 1859, 10th sess., ch. 108/pp. 98–99)
28 Apr 1860
TRINITY gained from MENDOCINO. (Calif. Stats. 1860, 11th sess., ch. 340/p. 334)
30 Oct 1872
TRINITY gained from MENDOCINO when their common boundary was surveyed; later MENDOCINO claimed a different boundary based on an 1891 survey. California Supreme Court upheld 1872 survey on 15 May 1907. (Calif. Stats. 1871, 19th sess., ch. 531/p. 766; "Trinity County v. Mendocino County," in Calif. Rpts., 151: 279–289)

TULARE

20 Apr 1852
TULARE created from MARIPOSA. (Calif. Stats. 1852, 3d sess., ch. 153/pp. 240–242)
30 Apr 1855
Legislature authorized creation of BUENA VISTA (proposed) from TULARE; creation did not take effect. (Calif. Stats. 1855, 6th sess., ch. 161/pp. 203–205; Coy, 15–16)
16 Apr 1856
Legislature authorized TULARE to lose to BUENA VISTA (proposed), even though the creation of BUENA VISTA (authorized 30 April 1855) had never gone into effect. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1856, 7th sess., ch. 81/p. 96)
19 Apr 1856
TULARE lost to creation of FREZNO (now FRESNO), gained from MERCED. (Calif. Stats. 1856, 7th sess., ch. 127/pp. 183)
04 Apr 1864
Legislature authorized creation of COSO from MONO and TULARE; creation did not take effect [see creation of INYO, 22 March 1866]. (Calif. Stats. 1863–1864, 15th sess., ch. 470/pp. 528–530)
22 Mar 1866
TULARE lost to creation of INYO; INYO boundaries were identical to those of COSO (proposed) [see 4 April 1864]. (Calif. Stats. 1865, 16th sess., ch. 316/pp. 355–358)
02 Apr 1866
TULARE lost to creation of KERN. (Calif. Stats. 1865, 16th sess., ch. 569/pp. 796–798)
10 Feb 1868
TULARE lost to KERN. (Calif. Stats. 1867, 17th sess., ch. 43/p. 40)
22 Jan 1870
TULARE lost to MONO the remnant of territory that was separated from TULARE by the creation of INYO on 22 March 1866. (Calif. Stats. 1869, 18th sess., ch. 18/p. 20)
01 Jan 1873
TULARE gained from KERN. (Political Code 1872, 1: secs. 3940–3941/pp. 138–139)
27 Mar 1874
TULARE exchanged with FRESNO. (Calif. Stats. 1873, 20th sess., ch. 468/p. 700)
23 Mar 1876
TULARE exchanged with FRESNO. (Calif. Stats. 1875, 21st sess., ch. 301/p. 397)
23 May 1893
TULARE lost to creation of KINGS. Act passed 22 March 1893; referendum for or against creation of new county held 23 May 1893. (Calif. Stats. 1893, 30th sess., ch. 150/pp. 176–181; Kings County History, http://calflytech.com/kingshistory.html, 18 July 2002)
31 Dec 1986
TULARE lost small area to FRESNO. Ordinance passed 18 November 1986; effective 31 December 1986 [change too small to display on interactive map; shapefile users see small_changes 1986_pt. for location]. (Minutes of the Board of Supervisors, Tulare County, 18 November 1986, ordinance 2745)
30 Sep 1991
TULARE exchanged small areas with FRESNO. Ordinance passed 3 September 1991; effective 30 September 1991 [change too small to display on interactive map; shapefile users see small_changes 1991_pt. for location]. (Minutes of the Board of Supervisors, Tulare County, 3 September 1991, ordinance 2970)

TUOLUMNE

18 Feb 1850
TUOLUMNE created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 27/p. 63)
18 Apr 1850
TUOLUMNE boundaries clarified [no change]. (Calif. Stats. 1849, 1st sess., ch. 111/pp. 262–263)
25 Apr 1851
TUOLUMNE boundaries redefined [no change]. (Calif. Stats. 1851, 2d sess., ch. 14, sec. 14/p. 175)
05 Apr 1854
TUOLUMNE lost to creation of STANISLAUS. (Calif. Stats. 1854, 5th sess., chs. 35, 81/pp. 40–41, 191–194)
04 May 1855
Boundary between TUOLUMNE and STANISLAUS clarified [no change]. (Calif. Stats. 1855, 6th sess., ch. 194/p. 245)
19 Apr 1856
TUOLUMNE lost to creation of FREZNO (now FRESNO). (Calif. Stats. 1856, 7th sess., ch. 127/pp. 183)
11 Apr 1859
TUOLUMNE gained from FREZNO (now FRESNO). (Calif. Stats. 1859, 10th sess., ch. 204/p. 213)
16 Mar 1864
TUOLUMNE lost to creation of ALPINE. (Calif. Stats. 1863–1864, 15th sess., ch. 180/pp. 178–182)

VENTURA

01 Jan 1873
VENTURA created from SAN LUIS OBISPO and SANTA BARBARA. Act passed 22 March 1872; took effect 1 January 1873. (Calif. Stats. 1871, 19th sess., ch. 351/pp. 484–489; Political Code 1872, 1: secs. 3946–3947/pp. 142–143)
Jul 1881
In July 1881, VENTURA gained from LOS ANGELES as a result of an official boundary survey. (Coy, 150–154, 292)
23 Jul 1919
VENTURA lost to KERN when boundary was adjusted to run on public land survey lines; legislature authorized VENTURA to exchange with LOS ANGELES. The California Supreme Court declared this chapter of the 1919 Political Code unconstitutional on 19 February 1920, but the VENTURA/KERN change appears to have remained in effect; change confirmed in 1923 by reenactment of the 1919 law. [Proposed change not displayed on interactive map; see "Special Topics."] (Calif. Stats. 1919, 43d sess., ch. 470, secs. 3923, 3964/pp. 870, 908–909; "Mundell v. Lyons," in Calif. Rpts., 182:289–293; Calif. Laws 1923, 45th sess., ch. 160, secs. 16, 57/pp. 336, 373; Coy, 152-153)
16 May 1923
VENTURA boundaries redefined; see 23 July 1919 [no change]. (Calif. Laws 1923, 45th sess., ch. 160, secs. 16, 57/pp. 336, 373)
31 Dec 1986
VENTURA lost small area to KERN [precise location unknown, not mapped]. (Minutes of the Board of Supervisors, Kern County, 4 November 1986, ordinance G–4345)
10 Jun 1991
VENTURA lost to KERN. (Calif. Stats. 1991–1992, reg. sess., ch. 51/p. 150)

YOLO

18 Feb 1850
YOLO created from non-county area. County was named "YOLA" in this act; by April 1850 the current spelling was in use. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 14/p. 61)
05 Apr 1850
YOLO boundaries clarified [no change]. (Calif. Stats. 1849, 1st sess., ch. 61, sec. 5/p. 156)
25 Apr 1851
YOLO lost to COLUSI (now COLUSA). (Calif. Stats. 1851, 2d sess., ch. 14, sec. 28/p. 179)
19 Apr 1856
YOLO lost to COLUSI (now COLUSA). (Calif. Stats. 1856, 7th sess., ch. 105/p. 124)
26 Mar 1857
YOLO gained from SOLANO. (Calif. Stats. 1857, 8th sess., ch. 104/p. 108)
03 Mar 1866
YOLO boundaries clarified [no change]. (Calif. Stats. 1865, 16th sess., ch. 181/p. 162; "Waters v. Pool," in Calif. Rpts., 130:136–139)
24 Mar 1868
YOLO lost to LAKE. (Calif. Stats. 1867, 17th sess., ch. 257/p. 269)
12 Mar 1870
YOLO lost small area to SACRAMENTO. (Calif. Stats. 1869, 18th sess., ch. 191/p. 294)
01 Jan 1980
YOLO gained small area from SOLANO. Ordinance passed 20 November 1979; effective 1 January 1980 [change too small to display on interactive map; shapefile users see small_changes 1980_pt. for location]. (Minutes of the Board of Supervisors, Solano County, 20 November 1979, ordinance 1085; Minutes of the Board of Supervisors, Yolo County, 20 November 1979, ordinance 861)
18 Dec 1992
YOLO gained small area from SOLANO [change too small to display on interactive map; shapefile users see small_changes 1992_pt. for location]. (Minutes of the Board of Supervisors, Solano County, 8 December 1992, ordinance 1460; Minutes of the Board of Supervisors, Yolo County, 24 November 1992, ordinance 1153)

YUBA

18 Feb 1850
YUBA created from non-county area. (Calif. Stats. 1849, 1st sess., ch. 15, sec. 20/p. 62)
25 Apr 1851
YUBA lost to SUTTER, and lost to creation of NEVADA and PLACER. (Calif. Stats. 1851, 2d sess., ch. 14, secs. 17, 19–20/pp. 176–177)
16 Apr 1852
YUBA lost to creation of SIERRA. (Calif. Stats. 1852, 3d sess., ch. 145/pp. 230–233)
22 Mar 1860
YUBA gained small area in village of Strawberry Valley from BUTTE [change too small to display on interactive map; shapefile users see small_changes 1860_pt. for location]. (Calif. Stats. 1860, 11th sess., ch. 145/p. 115)
15 Apr 1861
YUBA gained small area at Woodville from BUTTE [change too small to display on interactive map; shapefile users see small_changes 1861_pt. for location]. (Calif. Stats. 1861, 12th sess., ch. 166/p. 167)
13 Mar 1866
YUBA lost to SIERRA. (Calif. Stats. 1865, 16th sess., ch. 229/p. 228)
31 Mar 1866
YUBA lost small area to PLUMAS. (Calif. Stats. 1865, 16th sess., ch. 466/p. 605)
25 Feb 1897
YUBA exchanged with BUTTE. (Calif. Stats. 1897, 32d sess., ch. 26/p. 22)
09 Sep 1953
YUBA exchanged with SUTTER along Bear River. (Calif. Stats. 1953, reg. sess., ch. 836, sec. 2/pp. 2152–2156)
28 Mar 1994
YUBA gained small area from SUTTER [change too small to display on interactive map; shapefile users see small_changes 1994_pt. for location]. (Minutes of the Board of Supervisors, Yuba County, 20 July 1993, ordinance 1140)