Illinois Atlas of Historical County Boundaries
John H. Long, Editor; Peggy Tuck Sinko, Associate Editor; Gordon DenBoer, Historical Compiler; Douglas Knox, Book Digitizing Director and Digital Compiler; Emily Kelley, Research Associate; Laura Rico-Beck, GIS Specialist; Peter Siczewicz, ArcIMS Interactive Map Designer; Robert Will, Cartographic Assistant
Copyright The Newberry Library 2008
2 June 1609
King James I granted a new charter to the Virginia Company of London, expanding Virginia's jurisdiction westward and northwestward to the Pacific Ocean; included all of present Illinois. (Paullin, pl. 42; Swindler, 10:24-36; Van Zandt, 92)
10 February 1763
Treaty of Paris, ending the Seven Years' War between Great Britain (the victor) and France and Spain, formally transferred to the British all of Canada (territory north of the Ohio River-Great Lakes-St. Lawrence River line), including present Illinois, and implicitly set the Mississippi River as the new western limit for the British colonies. (Cappon, Petchenik, and Long, 1)
20 May 1774
The British Parliament passed the Quebec Act, placing all territory north and west of the Ohio River, including present Illinois, under the jurisdiction of the province of Quebec. (Cappon, Petchenik, and Long, 16, 87)
4 July 1776
The United States declared itself independent of Great Britain, implicitly opening the possibility that Virginia and some other states might claim territory north of the Ohio River and west of the Appalachian Mountains based on their colonial charters. (Declaration of Independence)
9 December 1778
ILLINOIS County (Va., extinct) created by Virginia to encompass all territory north and west of the Ohio River and east of the Mississippi River, including all of present Illinois. Virginia claimed this territory on the basis of its 1609 charter. (Hening, 9:552-555, 10:303-304; Robinson, 55)
3 September 1783
Commissioners from Great Britain and the United States signed the Treaty of Paris (ratifications exchanged 12 May 1784), ending the War of the American Revolution, recognizing American independence, and generally defining U.S. territory as extending to the Great Lakes-Lake of the Woods line on the north and the Mississippi River on the west, including present Illinois. (Parry, 48:481, 487, 491-492; Van Zandt, 12)
1 March 1784
All of present Illinois became unorganized federal territory when Virginia ceded its charter claims to the area to the United States. Other claims by Connecticut, Massachusetts, and New York to the area west of Pennsylvania were eliminated by 1786; ILLINOIS County (Va.) eliminated. (Cappon, Petchenik, and Long, 62, 130-131; Hening, 11:571-575)
13 July 1787
The United States created the Territory of the United States Northwest of the River Ohio (Northwest Territory) from unorganized federal territory. The Northwest Territory was to govern all territory west of Pennsylvania, north of the Ohio River, and east of the Mississippi River to which states had ceded their colonial charter claims, including all of present Illinois. (Terr. Papers U.S., 2:39-50)
27 April 1790
ST. CLAIR created by the Northwest Territory from non-county area in present Illinois. (Terr. Papers U.S., 3:301-303)
20 June 1790
KNOX (Ind.) created by the Northwest Territory from non-county area; included parts of present Illinois, Indiana, Michigan, Ohio, and Wisconsin. (Terr. Papers U.S., 3:313)
5 October 1795
RANDOLPH created by the Northwest Territory from ST. CLAIR. (Terr. Papers U.S., 3:441)
15 August 1796
WAYNE (Northwest Territory, extinct) created by the Northwest Territory from HAMILTON (Ohio), KNOX (Ind.), and non-county area in the Northwest Territory; WAYNE included a small area of present Illinois and parts of present Indiana, Michigan, Ohio, and Wisconsin. (Terr. Papers U.S., 2:567-568, 3:447)
22 June 1798
KNOX (Ind.) lost to HAMILTON (Ohio); KNOX's area within present Illinois was unchanged. (Terr. Papers U.S., 3:509)
4 July 1800
The United States created Indiana Territory from the Northwest Territory; included all of present Illinois and Wisconsin, and parts of present Michigan, Minnesota and Ohio; Northwest Territory eliminated. KNOX (Ind.), RANDOLPH, and ST. CLAIR became Indiana Territory counties; WAYNE (Northwest Territory, extinct) eliminated from present Illinois. (Terr. Papers U.S., 3:86-88; U.S. Stat., vol. 2, ch. 41 [1800]/pp. 58-59)
3 February 1801
As Indiana Territory counties, KNOX (Ind.) gained from non-county area in present Indiana, Michigan, and Ohio; lost to creation of CLARK (Ind.) and lost to RANDOLPH and ST. CLAIR; RANDOLPH gained from KNOX (Ind.) and ST. CLAIR; ST. CLAIR gained from KNOX (Ind.) and non-county area in present Illinois, Indiana, Michigan, Minnesota, and Wisconsin, and lost to RANDOLPH. (Ind. Terr., Exec. Journal, 97-100; Pence and Armstrong, 212, 520)
1 March 1803
Indiana Territory gained remainder of Northwest Territory when state of Ohio created; Northwest Territory eliminated. WAYNE (Indiana Territory, extinct) created by Indiana Territory from KNOX (Ind.), ST. CLAIR, and non-county area; included parts of present Illinois, Indiana, Michigan, Ohio, and Wisconsin. KNOX (Ind.) lost to HAMILTON (Ohio) and non-county area in Ohio; KNOX's area within present Illinois was unchanged. lost to creation of WAYNE (Indiana Territory, extinct), lost to HAMILTON (Ohio) and to non-county area in Ohio; KNOX's area within present Illinois was unchanged. (Ind. Terr., Exec. Journal, 114-115; Pence and Armstrong, 218; U.S. Stat., vol. 2, ch. 40 [1802], secs. 1-3/pp. 173-174; Van Zandt, 112)
1 May 1803
As Indiana Territory counties RANDOLPH exchanged with ST. CLAIR. (Ind. Terr., Exec. Journal, 117-118)
30 June 1805
The United States created Michigan Territory from Indiana Territory; eliminating WAYNE (Indiana Territory, extinct). The northeastern corner of present Illinois became non-county area in Indiana Territory. (Terr. Papers U.S., 10:5-7; U.S. Stat., vol. 2, ch. 5 [1805]/pp. 309-310)
1 December 1808
As Indiana counties, KNOX (Ind.) lost to creation of HARRISON (Ind.); KNOX's area within present Illinois was unchanged. (Ind. Terr. Laws, 1801-1809, 645-646)
1 March 1809
The United States created Illinois Territory from Indiana Territory; included all of present Illinois (except some small areas along the Wabash River), and parts of present Wisconsin, Michigan, and Minnesota. Former Indiana Territory counties of RANDOLPH and ST. CLAIR continued defacto, with no new boundaries specified [see 28 April 1809]; KNOX (Ind.) was effectively eliminated from Illinois, although some small areas of present Illinois along the Wabash River remained part of KNOX until 1816. (U.S. Stat., vol. 2, ch 13 [1809], sec. 1/pp. 514-515)
28 April 1809
RANDOLPH and ST. CLAIR created by Illinois Territory (effectively continuing the counties of the same name created by the Northwest Territory in 1795 and 1790 respectively). Net effect of the new boundaries: RANDOLPH gained from ST. CLAIR and gained the former area of KNOX (Ind.) that became part of Illinois Territory; RANDOLPH included a small area of present Indiana; ST. CLAIR exchanged with Indiana Territory. (Ill. Terr. Recs., 3-4; Terr. Papers U.S., 17:620-621)
14 September 1812
GALLATIN and JOHNSON created by Illinois Territory from RANDOLPH; boundary between GALLATIN and JOHNSON is estimated. MADISON created by Illinois Territory from RANDOLPH and ST. CLAIR; MADISON included territory in present Illinois, Wisconsin, Michigan, Minnesota, and a small area of Indiana. (Ill. Terr. Recs., 26; Terr. Papers U.S., 17:643)
11 December 1813
GALLATIN exchanged with RANDOLPH. (Ill. Terr. Laws, 120)
RANDOLPH exchanged with ST. CLAIR. (Ill. Terr. Laws, 120-121)
28 November 1814
EDWARDS created by Illinois Territory from GALLATIN and MADISON; EDWARDS included parts of present Illinois, Wisconsin, Michigan, and a small area of Indiana. (Ill. Terr. Laws, 128-130)
1 February 1816
WHITE created by Illinois Territory from GALLATIN; boundary with GALLATIN is estimated. (Ill. Terr. Laws, 185-186)
1 April 1816
JACKSON created by Illinois Territory from JOHNSON and RANDOLPH. (Ill. Terr. Laws, 215-217; Ill. Laws 1822-1823, pp. 122-123)
POPE created by Illinois Territory from GALLATIN and JOHNSON. (Ill. Terr. Laws, 217-219)
1 June 1816
MONROE created by Illinois Territory from RANDOLPH and ST. CLAIR. (Ill. Terr. Laws, 195-198)
11 December 1816
The state of Indiana created from Illinois, Indiana, and Michigan Territories; EDWARDS exchanged small areas along the Wabash River with the state of Indiana, establishing the boundary between the present states of Illinois and Indiana. (U.S. Stat., vol. 3, ch. 57 [1816], secs. 1-2/pp. 289-291, and res. 1 [1816]/pp. 399-400; Van Zandt, 115)
26 December 1816
POPE gained from GALLATIN. (Ill. Terr. Laws, 239)
31 December 1816
CRAWFORD created by Illinois Territory from EDWARDS; CRAWFORD included territory in present Illinois, Wisconsin, and Michigan. (Ill. Terr. Laws, 247-249)
4 January 1817
BOND created by Illinois Territory from MADISON; BOND included territory in present Illinois, Wisconsin, and Michigan. (Ill. Terr. Laws, 254-256)
2 January 1818
FRANKLIN created by Illinois Territory from GALLATIN, JOHNSON, and WHITE. (Ill. Terr. Laws, 290-291)
UNION created by Illinois Territory from JOHNSON; Non-County Area 1 created from JOHNSON and attached to UNION for administrative and judicial purposes; JOHNSON gained from POPE. (Ill. Terr. Laws, 292-294)
WASHINGTON created by Illinois Territory from ST. CLAIR. (Ill. Terr. Laws, 312-314)
6 January 1818
Boundary between MADISON and ST. CLAIR was redefined [no change]. (Ill. Terr. Laws, 311)
3 December 1818
The state of Illinois created from Illinois Territory, with present boundaries and the following counties: BOND, CRAWFORD, EDWARDS, FRANKLIN, GALLATIN, JACKSON, JOHNSON, MADISON, MONROE, POPE, RANDOLPH, ST. CLAIR, WASHINGTON, WHITE, and UNION. Michigan Terriotry gained remnants of Illinois Territory (present Wisconsin, western part of the Upper Peninsula of present Michigan, and the northeastern part of present Minnesota); BOND, CRAWFORD, and MADISON eliminated from present Michigan and Wisconsin. (Terr. Papers U.S., 10:803; U.S. Stat., vol. 3, ch. 67 [1818], secs. 1-2, 7/pp. 428-429, 431, and res. 1 [1818]/p. 536)
4 March 1819
ALEXANDER created from Non-County Area 1 attached to UNION; Non-County Area 1 eliminated. (Ill. Laws 1819, pp. 113-114)
22 March 1819
CLARK created from CRAWFORD. (Ill. Laws 1819, pp. 166-167)
26 March 1819
JEFFERSON created from EDWARDS and WHITE. (Ill. Laws 1819, pp. 267-268)
WAYNE created from EDWARDS. (Ill. Laws 1819, pp. 268-269)
29 March 1819
JEFFERSON gained from EDWARDS. (Ill. Laws 1819, pp. 320-321)
16 January 1821
LAWRENCE created from CRAWFORD and EDWARDS. (Ill. Laws 1820-1821, pp. 16-17)
20 January 1821
GREENE and Non-County Area 2 created from MADISON; Non-County Area 2 attached to GREENE "for all purposes." (Ill. Laws 1820-1821, pp. 26-27)
30 January 1821
SANGAMON created from BOND and MADISON. (Ill. Laws 1820-1821, pp. 45-46)
31 January 1821
PIKE created from BOND, CLARK, and MADISON. (Ill. Laws 1820-1821, p. 59)
8 February 1821
HAMILTON created from WHITE. (Ill. Laws 1820-1821, pp. 113-114)
12 February 1821
MONTGOMERY created from BOND and MADISON. (Ill. Laws 1820-1821, pp. 142-143)
14 February 1821
FAYETTE created from BOND, CLARK, CRAWFORD, JEFFERSON, and WAYNE. (Ill. Laws 1820-1821, pp. 164-167)
23 December 1822
CLARK gained small area from CRAWFORD. (Ill. Laws 1822-1823, p. 79)
30 December 1822
Non-County Area 3 created from PIKE; Non-County Area 3 attached to PIKE "until otherwise disposed of." (Ill. Laws 1822-1823, pp. 84-85)
3 January 1823
EDGAR created from CLARK. Non-County Area 4 created from CLARK and from part of Non-County Area 3 attached to PIKE; Non-County Area 4 attached to EDGAR for administrative and judicial purposes. (History of Edgar, 514-515; Ill. Laws 1822-1823, pp. 74-75)
24 January 1823
MARION created from FAYETTE and JEFFERSON. (Ill. Laws 1822-1823, pp. 49-50)
28 January 1823
FULTON created from Non-County Area 3 attached to PIKE. Non-County Area 5 created from Non-County Area 3 attached to PIKE; Non-County Area 5 attached to FULTON "until otherwise disposed of." (Ill. Laws 1822-1823, pp. 88-89)
31 January 1823
MORGAN created from SANGAMON and Non-County Area 2 attached to GREENE. (Ill. Laws 1822-1823, pp. 108-109; Ill. Laws 1834-1835, pp. 62-63)
23 December 1824
CLAY created from CRAWFORD, FAYETTE, LAWRENCE, and WAYNE. (Ill. Laws 1824-1825, pp. 18-20)
Non-County Area 6 created from SANGAMON. (Ill. Laws 1824-1825, pp. 20-22)
27 December 1824
CLINTON created from BOND, FAYETTE, and WASHINGTON. (Ill. Laws 1824-1825, pp. 27-30)
WABASH created from EDWARDS. (Ill. Laws 1824-1825, pp. 25-27)
3 January 1825
MADISON gained from Non-County Area 2 attached to GREENE. (Ill. Laws 1824-1825, p. 53)
10 January 1825
CALHOUN created from PIKE. (Ill. Laws 1824-1825, pp. 65-67)
13 January 1825
Legislature created nine new counties (Ill. Laws 1824-1825, pp. 85-87, 92-96)
ADAMS created from PIKE and Non-County Area 3 attached to PIKE.
HANCOCK created from Non-County Area 3 attached to PIKE; HANCOCK not fully organized, attached to ADAMS "for county purposes."
HENRY created from Non-County Area 5 attached to FULTON.
KNOX created from FULTON and Non-County Area 5 attached to FULTON.
MERCER and WARREN created from Non-County Area 3 attached to PIKE; MERCER was divided into two parts. MERCER and WARREN not fully organized, attached to SCHUYLER "for all county purposes."
PEORIA created from FULTON and Non-County Area 5 attached to FULTON. Non-County Area 6 attached to PEORIA "for county purposes."
PUTNAM created from Non-County Area 4 attached to EDGAR and Non-County Area 5 attached to FULTON.
SCHUYLER created from FULTON, PIKE, and Non-County Area 3 attached to PIKE. MERCER and WARREN were attached to SCHUYLER. Non-County Area 3 detached from PIKE, attached to SCHUYLER. All attachments were "for all county purposes."
15 January 1825
MONROE gained from ST. CLAIR. (Ill. Laws 1824-1825, pp. 109-110)
18 January 1826
VERMILION created from CLARK and Non-County Area 4 attached to EDGAR; Non-County Area 4 detached from EDGAR, attached to VERMILION "for all county purposes." (Ill. Laws 1826, pp. 50-53)
25 January 1826
McDONOUGH created from all of Non-County Area 3 attached to SCHUYLER; Non-County Area 3 eliminated. McDONOUGH not fully organized, attached to SCHUYLER "for county purposes." (Ill. Laws 1826, pp. 76-77)
1 March 1826
MERCER and WARREN detached from SCHUYLER, attached to PEORIA "for county purposes." (Ill. Laws 1826, pp. 76-77)
9 January 1827
MONROE gained from ST. CLAIR. (Ill. Laws 1826-1827, pp. 7-8)
23 January 1827
MONTGOMERY gained from FAYETTE. SHELBY and Non-County Area 7 created from FAYETTE; Non-County Area 7 attached to SHELBY "until otherwise provided by law." (Ill. Rev. Code 1826-1827, pp. 115-117)
29 January 1827
PERRY created from JACKSON and RANDOLPH. (Ill. Rev. Code 1826-1827, pp. 110-113)
31 January 1827
TAZEWELL created from Non-County Area 6 attached to PEORIA and Non-County Area 7 attached to SHELBY. Non-County Area 6 gained from Non-County Area 7; Non-Cunty Area 6 detached from PEORIA, attached to TAZEWELL for administrative and judicial purposes. (Ill. Rev. Code 1826-1827, pp.113-115; Ill. Rev. Code 1828-1829, p. 32)
17 February 1827
JO DAVIESS created from HENRY, MERCER, and PUTNAM. (Ill. Rev. Code 1826-1827, pp. 117-118)
17 January 1829
MACOUPIN created from MADISON and all of Non-County Area 2 attached to GREENE; Non-County Area 2 eliminated. (Ill. Rev. Code 1828-1829, pp. 26-28)
19 January 1829
MACON created from all of Non-County Area 7 attached to SHELBY; Non-County Area 7 eliminated. (Ill. Rev. Code 1828-1829, pp. 28-31)
20 January 1829
Boundary between MONROE and RANDOLPH was clarified [no change]. (Ill. Rev. Code 1828-1829, pp. 31-32)
22 January 1829
Boundaries of EDWARDS and WAYNE clarified [no change]. (Ill. Rev. Code 1828-1829, p. 32)
3 August 1829
HANCOCK fully organized, detached from ADAMS. (Scofield, 679)
3 July 1830
McDONOUGH fully organized, detached from SCHUYLER. (McLean, 624)
25 December 1830
COLES created from CLARK and EDGAR. (Ill. Laws 1830-1831, pp. 59-61)
McLEAN created from TAZEWELL and Non-County Area 6 attached to TAZEWELL. (Ill. Laws 1830-1831, pp. 57-59)
15 January 1831
Legislature created two new counties and revised the boundaries of other counties (Ill. Laws 1830-1831, pp. 54-57, 62-63)
COOK created from PUTNAM.
HENRY gained from JO DAVIESS and PUTNAM, lost to KNOX; HENRY attached to KNOX "for all judicial and other purposes."
KNOX gained from HENRY and PUTNAM.
LA SALLE created from PUTNAM, Non-County Area 4 attached to VERMILION, and Non-County Area 6 attached to TAZEWELL.
PUTNAM gained from JO DAVIESS and Non-County Area 6 attached to TAZEWELL; lost to creation of COOK, LA SALLE, and Non-County Areas 8 and 9; and lost to HENRY and KNOX.
Non-County Area 8 created from part of PUTNAM; Non-County Area 8 attached to LA SALLE for administrative and judicial purposes.
Non-County Area 9 created from part of PUTNAM.
27 January 1831
WARREN fully organized, detached from PEORIA. MERCER detached from PEORIA, attached to WARREN "for all judicial and other purposes." (Ill. Laws 1830-1831, pp. 67-68)
9 February 1831
ROCK ISLAND created from JO DAVIESS; ROCK ISLAND not fully organized, attached to JO DAVIESS "for all judicial and other county purposes." (Ill. Laws 1830-1831, pp. 52-53)
15 February 1831
EFFINGHAM created from CRAWFORD and FAYETTE; EFFINGHAM not fully organized, parts attached to CRAWFORD and FAYETTE until "organized." JASPER created from CLAY and CRAWFORD; JASPER not fully organized, parts attached to CLAY and CRAWFORD until "organized." (Ill. Laws 1830-1831, pp. 50-52)
20 December 1832
EFFINGHAM fully organized, detached from CRAWFORD and FAYETTE. (Ill. Laws 1832-1833, pp. 22-23)
20 February 1833
CHAMPAIGN created from VERMILION and Non-County Area 4 attached to VERMILION. (Ill. Laws 1832-1833, priv., pp. 28-30)
26 February 1833
IROQUOIS created from Non-County Area 9, and from Non-County Area 4 attached to VERMILION; IROQUOIS not fully organized, attached to VERMILION "for judicial and other county purposes." (Ill. Laws 1832-1833, priv., pp. 19-20)
VERMILION gained part of attached Non-County Area 4. (Ill. Laws 1832-1833, priv., pp. 19-20)
1 March 1833
ROCK ISLAND fully organized, detached from JO DAVIESS. (Ill. Laws 1832-1833, priv., pp. 17-18)
24 February 1834
IROQUOIS fully organized, detached from VERMILION. (Beckwith, Iroquois, 343)
19 December 1834
JASPER fully organized, detached from CLAY and CRAWFORD. (Ill. Laws 1834-1835, pp. 154-155)
31 January 1835
MERCER fully organized, detached from WARREN. (Ill. Laws 1835-1835, p. 156)
1 March 1835
FRANKLIN exchanged with PERRY. (Ill. Laws 1834-1835, pp. 36-37)
12 January 1836
WILL created from COOK, IROQUOIS, Non-County Area 4 attached to VERMILION, and all of Non-County Area 9; Non-County Area 9 eliminated. (Ill. Laws 1835-1836, pp. 262-263)
16 January 1836
Legislature created five new counties: (Ill. Laws 1835-1836, 273-278)
KANE created from Non-County Area 8 attached to LA SALLE.
McHENRY created from COOK and Non-County Area 8 attached to LA SALLE; McHENRY not fully organized, attached to COOK until "organized".
OGLE and WINNEBAGO created from JO DAVIESS and Non-County Area 8 attached to LA SALLE.
WHITESIDE created from HENRY and JO DAVIESS; WHITESIDE not fully organized, attached to JO DAVIESS until "organized."
Non-County Area 8 gained small area from JO DAVIESS; Non-County Area 8 effectively detached from LA SALLE.
24 December 1836
WHITESIDE detached from JO DAVIESS, attached to OGLE "for all judicial and county purposes." (History of Ogle, 299-300; Ill. Laws 1835-1836, p. 277)
27 February 1837
LIVINGSTON created from LA SALLE, McLEAN, and Non-County Area 4 attached to VERMILION. (Ill. Laws 1836-1837, pp. 83-85)
1 March 1837
Legislature authorized creation of COFFEE (proposed) from HENRY, KNOX, and PUTNAM, dependent on local referendum that failed. COFFEE was in the same general area as STARK, created 2 March 1839. (Ill. Laws 1836-1837, pp. 86-88)
McHENRY fully organized, detached from COOK; McHENRY's boundaries were extended to the Illinois state limits in Lake Michigan [not mapped]. (Ill. Laws 1836-1837, pp. 89-90)
2 March 1837
Legislature authorized creation of MICHIGAN (proposed) from COOK, dependent on local referendum that failed. MICHIGAN was in the same general area as DU PAGE, created 9 February 1839. (Ill. Laws 1836-1837, pp. 82-83)
3 March 1837
Boundaries of ADAMS, HANCOCK, MERCER, and WARREN were extended to the middle of the Mississippi River [not mapped]. (Ill. Laws 1836-1837, pp. 91-92)
4 March 1837
BOONE created from WINNEBAGO; STEPHENSON created from JO DAVIESS and WINNEBAGO. (Ill. Laws 1836-1837, pp. 96-100)
Boundary between HENRY and KNOX was clarified [no change]. (Ill. Laws 1836-1837, p. 89)
3 April 1837
BUREAU created from PUTNAM. (Ill. Laws 1836-1837, pp. 93-95)
17 April 1837
CASS created from MORGAN. (Ill. Laws 1836-1837, pp. 101-103; Ill. Laws 1837, spec. sess., pp. 48-50)
1 May 1837
DE KALB created from KANE. (Ill. Laws 1836-1837, pp. 96-100)
19 June 1837
HENRY fully organized, detached from KNOX. (Ill. Laws 1836-1837, pp. 90-91)
19 January 1839
BUREAU gained all of Non-County Area 8 (remnant of JO DAVIESS and non-county area previously attached to LA SALLE); Non-County Area 8 eliminated. MARSHALL created from PUTNAM. (Ill. Laws 1838-1839, pp. 43-45)
1 February 1839
BROWN created from SCHUYLER. (Ill. Laws 1838-1839, pp. 52-55)
9 February 1839
DU PAGE created from COOK. On 2 March 1837, an unsuccessful attempt was made to create MICHIGAN (proposed) in the same general area. (Ill. Laws 1838-1839, pp. 73-74)
15 February 1839
DANE (now CHRISTIAN) created from MONTGOMERY and SANGAMON; LOGAN and MENARD created from SANGAMON. (Ill. Laws 1838-1839, pp. 104-107)
16 February 1839
SCOTT created from MORGAN. (Ill. Laws 1838-1839, pp. 126-130)
21 February 1839
WHITESIDE fully organized, detached from OGLE. (Ill. Laws 1838-1839, pp. 143-144)
22 February 1839
CARROLL created from JO DAVIESS; OGLE gained from JO DAVIESS. (Ill. Laws 1838-1839, pp. 160-162)
26 February 1839
DANE (now CHRISTIAN) gained from SHELBY. (Ill. Laws 1838-1839, pp. 187-188)
27 February 1839
LEE created from OGLE. (Ill. Laws 1838-1839, pp. 170-172)
1 March 1839
DE WITT created from McLEAN and MACON. (Ill. Laws 1838-1839, pp. 199-201)
LAKE created from McHENRY. (Ill. Laws 1838-1839, pp. 216-217)
2 March 1839
Legislature authorized BOONE to gain from McHENRY townships 43 to 46 north, range 5 east, dependent on local referendum that failed [no change]. (Ill. Laws 1838-1839, p. 242)
BUREAU gained from PUTNAM. (Ill. Laws 1838-1839, p. 229)
MACON gained from SANGAMON. (Ill. Laws 1838-1839, p. 265)
Legislature authorized MARSHALL and PUTNAM to gain from LA SALLE townships 29 to 32, and township 33 south of the Big Vermilion River, range 1 east, dependent on local referendum that failed [no change]. (Ill. Laws 1838-1839, p. 241)
STARK created from PUTNAM. On 1 March 1837, an unsuccessful attempt was made to create COFFEE (proposed) in the same general area. (Ill. Laws 1838-1839, pp. 229-232)
18 March 1839
STARK gained from KNOX. (Ill. Laws 1838-1839, pp. 229-230)
August 1839
Legislature authorized DU PAGE to gain the northern halves of township 37 north, ranges 9 and 10 east, from WILL, dependent on local referendum that failed [no change]. (History of Will, 358-359; Ill. Laws 1838-1839, pp. 73-74)
5 August 1839
HARDIN created from POPE. (Ill. Laws 1838-1839, pp. 234-236)
JERSEY created from GREENE. (Ill. Laws 1838-1839, pp. 208-211)
WILLIAMSON created from FRANKLIN. (Ill. Laws 1838-1839, pp. 110-113)
In August 1839, the legislature authorized DU PAGE to gain from WILL the northern half of township 37 north, ranges 9 and 10 east, dependent on local referendum that failed [no change]. (History of Will, 358-359; Ill. Laws 1838-1839, pp. 73-74)
8 January 1840
POPE gained from HARDIN. (Ill. Laws 1839-1840, spec. sess., pp. 38-40)
27 January 1840
LOGAN gained from TAZEWELL. (Ill. Laws 1839-1840, spec. sess., p. 29)
1 February 1840
DANE renamed CHRISTIAN. (Ill. Laws 1839-1840, spec. sess., p. 80)
Legislature authorized STARK to gain from HENRY all of township 14 north, range 5 east; and parts of township 14 north, range 4 east, and township 15 north, ranges 4 and 5 east, dependent on local referendum that failed [no change]. (Ill. Laws 1839-1840, spec. sess., pp. 62-63)
20 January 1841
HENDERSON created from WARREN. (Ill. Laws 1840-1841, pp. 67-69)
MASON created from MENARD and TAZEWELL. (Ill. Laws 1840-1841, pp. 69-71)
27 January 1841
PIATT created from DE WITT and MACON. (Ill. Laws 1840-1841, pp. 71-74)
17 February 1841
GRUNDY created from LA SALLE. (Ill. Laws 1840-1841, pp. 74-75)
19 February 1841
Legislature authorized BOND to gain from MADISON the eastern halves of townships 4 to 6 north, range 5 west, dependent on local referendum that failed [no change]. (Ill. Laws 1840-1841, p. 80)
KENDALL created from KANE and LA SALLE. (Ill. Laws 1840-1841, pp. 75-77)
24 February 1841
Legislature authorized creation of OKAW (proposed) from MACON and SHELBY, dependent on local referendum that failed. OKAW was in the same general area as MOULTRIE, created 16 February 1843. (Ill. Laws 1840-1841, pp. 80-83)
27 February 1841
Legislature authorized creation of ALLEN (proposed) from MACOUPIN, MORGAN, and SANGAMON, dependent on local referendum that failed. Subsequent attempts were made to create a county in the same general area (BENTON in 1843 and OREGON in 1851), but all attempts failed. (Ill. Laws 1840-1841, pp. 87-90)
Legislature authorized CARROLL to gain from OGLE the eastern halves of townships 23 to 25 north, range 7 east, dependent on local referendum that failed [no change]. (Ill. Laws 1840-1841, p. 90)
WOODFORD created from McLEAN and TAZEWELL. (Ill. Laws 1840-1841, pp. 84-86)
7 June 1841
RICHLAND created from CLAY and LAWRENCE. (Ill. Laws 1840-1841, pp. 77-79)
6 February 1843
Legislature authorized creation of AUDUBON (proposed) from FAYETTE, MONTGOMERY, and SHELBY, dependent on local referendum that failed. (Ill. Laws 1842-1843, pp. 73-74)
8 February 1843
MASSAC created from JOHNSON and POPE. (Ill. Laws 1842-1843, pp. 74-76)
11 February 1843
MARQUETTE (later HIGHLAND, extinct) created from ADAMS. (Ill. Laws 1842-1843, pp. 77-83)
16 February 1843
MOULTRIE created from MACON and SHELBY. On 24 February 1841, an unsuccessful attempt was made to create OKAW (proposed) in the same general area. (Ill. Laws 1842-1843, pp. 83-85)
17 February 1843
Legislature authorized WOODFORD to gain from TAZEWELL all of township 26 north, east of the Illinois River (except for small area around East Peoria), dependent on local referendum that failed [no change]. (Ill. Laws 1842-1843, pp. 86-88)
21 February 1843
Legislature authorized creation of MILTON (proposed) from VERMILION, dependent on local referendum that failed [no change]. (Ill. Laws 1842-1843, pp. 88-91)
24 February 1843
McHENRY boundaries were redefined [no change]. (Ill. Laws 1842-1843, p. 91)
28 February 1843
McLEAN exchanged with WOODFORD. (Ill. Laws 1842-1843, p. 91)
2 March 1843
BOND gained from MADISON. (Ill. Laws 1842-1843, pp. 98-99)
MENARD gained from SANGAMON. (Ill. Laws 1842-1843, p. 94)
3 March 1843
POPE gained from MASSAC. (Ill. Laws 1842-1843, p. 101)
4 March 1843
Boundaries of all counties bordering the Wabash and Mississippi Rivers were extended to the state limit in those rivers [not mapped]. (Ill. Laws 1842-1843, p. 109)
Legislature authorized creation of BENTON (proposed) from GREENE, MACOUPIN, and MORGAN, dependent on local referendum that failed. Other attempts to create counties in the same general area (ALLEN in 1841; OREGON in 1851) were also unsuccessful. (Ill. Laws 1842-1843, pp. 104-108)
Legislature authorized CASS to gain from MORGAN the southern half of township 17 north all along its southern border, dependent on local referendum that failed [no change]; the transfer was approved in a second referendum, on 5 May 1845. (Ill. Laws 1842-1843, pp. 104-108)
12 April 1843
MARSHALL gained from LA SALLE. (Ill. Laws 1842-1843, pp. 93-94)
1 May 1843
CUMBERLAND created from COLES. (Ill. Laws 1842-1843, pp. 94-98)
22 May 1843
BOONE gained from WINNEBAGO. (Ill. Laws 1842-1843, p. 92)
5 June 1843
PULASKI created from ALEXANDER and MASSAC. (Ill. Laws 1842-1843, pp. 99-101)
26 February 1845
Legislature authorized EFFINGHAM to gain from SHELBY the northern half of township 9 north, ranges 4 to 6 east, dependent on local referendum that failed [no change]. (Ill. Laws 1844-1845, p. 164)
LOGAN gained from DE WITT. (Ill. Laws 1844-1845, p. 189)
28 February 1845
FULTON and PEORIA each gained part of small Non-County Area 5 ("the gore"); Non-County Area 5 eliminated. (Ill. Laws 1844-1845, p. 267)
5 May 1845
CASS gained from MORGAN. (Ill. Laws 1844-1845, pp. 313-315)
20 February 1847
HARDIN gained from GALLATIN. (Ill. Laws 1846-1847, priv. and spec., pp. 30-31)
27 February 1847
MARQUETTE renamed HIGHLAND (extinct); HIGHLAND (extinct) gained from ADAMS. (Ill. Laws 1846-1847, gen., pp. 38-41)
28 February 1847
MENARD gained from SANGAMON. (Ill. Laws 1846-1847, priv. and spec., p. 39)
2 August 1847
SALINE created from GALLATIN by local referendum. (Ill. Laws 1846-1847, priv. and spec., pp. 34-37)
by 31 December 1848
ADAMS gained all of HIGHLAND (extinct) when HIGHLAND failed to become fully organized as a county; HIGHLAND eliminated. (Wilcox, David F., 1:119-120)
8 February 1849
Legislature authorized ROCK ISLAND to gain from MERCER township 15 north, ranges 1 and 2 west, dependent on local referendum that failed [no change]. (Ill. Laws 1849, 1st sess., gen., pp. 51-52)
12 February 1849
Legislature authorized STARK to gain from HENRY either all of township 14 north, range 5 east, or just the southern half thereof, dependent on local referendum that failed [no change]. (Ill. Laws 1849, 1st sess., gen., pp. 55-56)
11 February 1851
Legislature authorized creation of KANKAKEE (proposed) from IROQUOIS and WILL, dependent on local referendum that failed; second attempt to create KANKAKEE on 5 April 1853, with slightly different boundaries, was successful. (Ill. Laws 1851, gen., pp. 30-35)
15 February 1851
Legislature authorized creation of OREGON (proposed) from MACOUPIN, MORGAN, and SANGAMON, dependent on local referendum that failed. Previous attempts to create counties in the same general area (ALLEN in 1841 and BENTON in 1843) were also unsuccessful. (Ill. Laws 1851, gen., pp. 131-134)
Legislature authorized PUTNAM to gain from LA SALLE townships 31 and 32 north, range 1 east, dependent on local referendum that failed [no change]. (Ill. Laws 1851, gen., pp. 111-112)
Legislature authorized SHELBY to gain from CHRISTIAN township 11 north, range 1 east, dependent on local referendum that failed [no change]. (Ill. Laws 1851, gen., pp. 118-119)
3 March 1851
GREENE exchanged with JERSEY. (Ill. Laws 1851, gen., pp. 145-146)
28 April 1851
GALLATIN gained all of SALINE when SALINE was abolished by the state legislature. (History of Gallatin, Saline, 66-67; Ill. Laws 1851, gen., pp. 28-29)
2 August 1852
SALINE re-created from GALLATIN by local referendum. (History of Gallatin, Saline, 66-67; Ill. Laws 1852, pp. 106-108; Ill. Rpts., 12:391-397)
5 April 1853
KANKAKEE created from IROQUOIS and WILL. Boundaries were somewhat different from KANKAKEE (proposed) authorized on 11 February 1851. (Ill. Laws 1853, gen., pp. 159-163)
4 March 1854
ROCK ISLAND exchanged with WHITESIDE. (Ill. Laws 1853, priv., p. 462; Ill. Laws 1854, priv., pp. 161-162)
7 November 1854
HAMILTON gained from SALINE; WHITE gained from GALLATIN. (History of Gallatin, Saline, 42-43; Ill. Laws 1853, gen., pp. 265-266; Ill. Laws 1854, priv., pp. 143-144)
14 February 1855
Legislature authorized creation of HARRISON (proposed) from CHAMPAIGN, McLEAN, and Non-County Area 4 attached to VERMILION, dependent on local referendum that failed [no change]. (Ill. Laws 1855, pub., pp. 113-117)
4 June 1855
KANKAKEE gained from Non-County Area 4 attached to VERMILION. (Ill. Laws 1855, priv., pp. 662-663)
31 January 1857
Legislature authorized creation of HOLMES (proposed) from CHAMPAIGN, VERMILION, and Non-County Area 4 attached to VERMILION, dependent on local referendum that failed. HOLMES was in the same general area as FORD, which was created 5 April 1859. (Ill. Laws 1857, pub., pp. 93-98)
13 February 1857
Legislature authorized creation of DOUGLAS (proposed) from CHAMPAIGN and COLES, dependent on local referendum that failed. DOUGLAS was created, with slightly different boundaries, on 21 March 1859. (Ill. Laws 1857, pub., pp. 71-74)
21 March 1859
DOUGLAS created from COLES. An earlier attempt on 13 February 1857 to create DOUGLAS, with slightly different boundaries, failed [see DOUGLAS (proposed)] . (Ill. Laws 1859, pub., pp. 24-29)
5 April 1859
FORD created from all of Non-County Area 4 attached to VERMILION; Non-County Area 4 eliminated. An earlier attempt to create HOLMES (proposed), on 31 January 1857 in the same general area, was unsuccessful. (Ill. Laws 1859, pub., pp. 29-33)
21 February 1863
Legislature authorized CLAY to gain from WAYNE the southern half of township 2 north, ranges 5 to 8 east, dependent on local referendum that failed [no change]. (Ill. Laws 1863, pub., pp. 84-85)
8 March 1867
Legislature authorized KANKAKEE to gain from IROQUOIS the remainder of township 29 north all along its southern boundary, dependent on local referendum that failed [no change]. (Ill. Laws 1867, priv., 3:632-634)
9 July 1867
Legislature authorized creation of LINCOLN (proposed) from VERMILION and CHAMPAIGN, dependent on local referendum that failed [no change]. (Ill. Laws 1867, priv., 1:868-873)
29 March 1869
ROCK ISLAND exchanged with WHITESIDE (repealed act of 4 March 1854). (Ill. Laws 1869, pub., pp. 94-95, 161)