Arizona: Consolidated Chronology of State and County Boundaries

22 February 1819

All of present Arizona came under Spanish control when the Adams-Onis Treaty between the United States and Spain established the boundary between the two countries from the Gulf of Mexico to the Pacific Ocean. Ratifications exchanged 22 February 1821. (Parry, 70:1-30; Van Zandt, 26-27)

24 August 1821

Mexico gained its independence from Spain; present Arizona became part of the Republic of Mexico. (Beers, 100; "Mexican War of Independence," New Handbook of Texas, 4:698)

12 January 1828

Treaty of Limits between Mexico and the United States defined the boundary between the two countries to be the same as established by the 1819 Adams-Onis Treaty with Spain. (Parry, 78:35-42; Van Zandt, 121)

13 May 1846

Following a series of boundary skirmishes, and repeated attempts by Texas to claim all that portion of Mexico located between the Nueces River and the Rio Grande River, Congress declared a state of war between the United States and Mexico. (U.S. Stat., vol. 9, ch. 16[1846]/pp. 9-10; Williams 108-110)

18 August 1846

The U.S. Army of the West, under command of Brigadier General Stephen Watts Kearny, took control of Santa Fe (N.M.) and proclaimed United States sovereignty over the southwest territory of New Mexico (Mexico). (Williams 108-110)

22 September 1846

Kearny's Code of Laws was promulgated in Santa Fe for use in the occupied Mexican territory. Code included a Bill of Rights, Laws for the Government of the Territory of New Mexico, and established civil and judicial appointments for the seven original counties of: BERNALILLO (N.M.), RIO ARRIBA (N.M.), SAN MIGUEL (N.M.), SANTA FE (N.M.), SANTA ANA (N.M., extinct), TAOS (N.M.), and VALENCIA (N.M.). (Kearny's Code 1846, "Courts and Judicial Powers", secs. 5-7/p. 49; Abel, Map #2; Coan, 252; Williams, 108-109)

04 July 1848

Treaty of Guadalupe-Hidalgo ended the war between Mexico and the United States. Area ceded by Mexico became Unorganized Federal Territory in the United States; included all of present California, Nevada, and Utah, and parts of present Arizona, Colorado, New Mexico, and Wyoming. Mexico retained parts of present Arizona and New Mexico; Part of the international boundary was in dispute. Treaty was signed 3 February 1848, proclaimed 4 July 1848. (U.S. Stat., vol. 9, pp. 922-943; Parry, 102: 29-59; Van Zandt, 11, 28-29; Walker and Bufkin, 19, 20A)

13 December 1850

The United States created New Mexico Territory from Unorganized Federal Territory (land ceded by Mexico in the Treaty of Guadalupe-Hidalgo), and from land purchased from the state of Texas; included most of present Arizona and New Mexico, and parts of present Colorado and Nevada. Faulty geographic information on the Disturnell map referenced in the treaty led to a dispute between the United States and Mexico over the exact location and extent of the international boundary. All that portion of New Mexico Territory lying outside the boundaries of the seven original counties established under Kearny's Code became non-county area; included most of present Arizona and New Mexico, and parts of present Colorado and Nevada. The portion of Arizona south of the Gila River remained part of Mexico. (U.S. Stat., vol. 9, ch. 49[1850]/pp. 446-452; Baldwin, 117-137; Coffey, 145-164; Van Zandt, 28-29, 162-165)

09 January 1852

New Mexico legislature passed a single act creating two new counties, redefining five of the original counties to extend across the limits of the territory, and eliminating all non-county area. (N.M. Terr. Laws 1851, 1st assy., 1st sess./p. 119; N.M. Terr. Laws 1851, 1st assy., 2d sess. /pp. 266, 292; for pages on particular counties, see following citations)

DOÑA ANA (N.M.) and SOCORRO (N.M.) created from non-county area; included parts of present Arizona and New Mexico. (pp. 266, 292)

BERNALILLO (N.M.) gained from VALENCIA (N.M.) and non-county area, exchanged with SAN MIGUEL (N.M.), and lost to SANTA ANA (N.M.) and SANTA FE (N.M.) when all counties redefined; included parts of present Arizona, Nevada and New Mexico. (p. 292)

RIO ARRIBA (N.M.) gained from SAN MIGUEL (N.M.), SANTA ANA (N.M.), SANTA FE (N.M.) and non-county area, and exchanged with TAOS (N.M.) when all counties redefined; included parts of present Arizona, Nevada and New Mexico. (p. 291)

SANTA ANA (N.M. Territory, extinct) gained from BERNALILLO (N.M.) and non-county area, exchanged with SANTA FE (N.M.), and lost to RIO ARRIBA (N.M.) when all counties redefined; included parts of present Arizona, Nevada, and New Mexico. (p. 292)

TAOS (N.M.) gained from non-county area, and exchanged with RIO ARRIBA (N.M.) and SAN MIGUEL (N.M.) when all counties redefined; included parts of present Arizona, Colorado, Nevada and New Mexico. (p. 291)

VALENCIA (N.M.) gained from non-county area, lost to creation of SOCORRO (N.M.), and lost to BERNALILLO (N.M.) when all counties redefined; included parts of present Arizona, Nevada, and New Mexico. (p. 292)

30 December 1853

Gadsden Purchase settled the boundary dispute between the United States and Mexico and established the international line at its present location. (U.S. Stat., vol. 10, pp. 1031-1037; Van Zandt, 11, 29, 162)

04 August 1854

Non-county area was created in New Mexico Territory when the land acquired by the United States in the Gadsden Purchase was officially added to the territory without being assigned to a county. Most of the non-county area was located in present Arizona. (U.S. Stat., vol. 10, ch. 245[1854]/p. 575; Van Zandt, 162; Walker and Bufkin, 21-22)

03 February 1855

DOÑA ANA (N.M.) gained all of non-county area (Gadsden Purchase) in New Mexico Territory; non-county area eliminated. (N.M. Terr. Laws 1854, 4th assy. /p. 57)

01 February 1860

ARIZONA (N.M. Territory, extinct) created by New Mexico Territory from DOÑA ANA (N.M.). ARIZONA (extinct) was located entirely within present Arizona. (N.M. Terr. Laws 1859-1860, 9th assy. /p. 74)

TAOS (N.M.) lost to creation of MORA (N.M.); the part of TAOS in present Arizona was unchanged. (N.M. Terr. Laws 1859-1860, 9th assy. /p. 76)

05 April 1860

An unofficial convention held in Tucson established a provisional government, declared the creation of the Territory of Arizona from all that part of New Mexico Territory that lay south of 33 degrees 40 minutes north latitude, and authorized the creation of CASTLE DOME (proposed), DOÑA ANA (proposed), EWELL (proposed), and MESILLA (proposed). Congress failed to recognize the new territory and its proposed counties [no change]. (Sacks, 36, 151; Swindler, 1:244-248)

12 January 1861

SAN JUAN (N.M. Territory, original, extinct) created by New Mexico Territory from TAOS (N.M.); included parts of present Arizona, New Mexico, and Nevada. (N.M. Terr. Laws 1860-1861, 10th assy. /p. 16)

28 February 1861

TAOS (N.M.) lost to creation of Colorado Territory; the part of TAOS in present Arizona was unchanged. (U.S. Stat., vol. 12, pp. 172-177; Van Zandt, 141-144)

18 January 1862

DOÑA ANA (N.M.) gained all of ARIZONA (N.M. Territory, extinct); ARIZONA eliminated. (N.M. Terr. Laws 1861-1862, 11th assy. /p. 18)

TAOS (N.M.) gained all of SAN JUAN (N.M. Territory, original, extinct); SAN JUAN eliminated. (N.M. Terr. Laws 1861-1862, 11th assy. /p. 16)

28 January 1863

ARIZONA (N.M. Territory, extinct) re-created from DOÑA ANA (N.M.). (N.M. Terr. Laws 1862-1863, 12th assy. /p.30)

24 February 1863

Arizona Territory created by the United States from the western portion of New Mexico Territory and a part of present Nevada. Arizona did not immediately created any counties. BERNALILLO (N.M.), DOÑA ANA (N.M.), RIO ARRIBA (N.M.), SANTA ANA (N.M. Territory, extinct), SOCORRO (N.M.), TAOS (N.M.) and VALENCIA (N.M.) all eliminated from Arizona Territory, ARIZONA (N.M. Territory, extinct) eliminated entirely. (U.S. Stat., vol. 12, ch. 56[1863]/pp. 664-665; Ariz. Terr. Laws 1864, 1st assy./ pp. vii-viii; Van Zandt, 162)

10 November 1864

Arizona Territory passed a single act creating the four original counties of: MOHAVE (which included part of present Nevada), PIMA, YAVAPAI, and YUMA. (Howell Code, Ariz. Terr. Laws 1864, 1st assy., ch. 2/ pp. 24-25)

22 December 1865

PAH-UTE (extinct) created by Arizona Territory from MOHAVE; included part of present Nevada. (Ariz. Terr. Laws 1865, 2d assy./ pp. 19-20)

05 May 1866

State of Nevada gained parts of MOHAVE and PAH-UTE (extinct) when the United States transferred the portion of Arizona Territory lying between 37 degrees and 42 degrees of north latitude and west of 114 degrees west longitude to Nevada. Arizona twice petitioned Congress (5 May 1866 and 5 October 1867) to repeal the act of transfer and did not officially recognize the loss until 18 February 1871 when a change to the boundaries of MOHAVE implicitly acknowledged the new Arizona - Nevada line. (U.S. Stat., vol. 14, ch. 73[1866]/p. 43; Van Zandt, 158, 165; Ariz. Terr. Laws 1867, 3rd assy./ pp. 67-68; Ariz. Terr. Laws 1868, 4th assy./ pp. 68-69)

14 February 1871

MARICOPA created by Arizona Territory from YAVAPAI. (Ariz. Terr. Laws 1871, 6th assy./ pp. 53-54)

18 February 1871

MOHAVE gained all of PAH-UTE (extinct) when the law creating PAH-UTE was repealed. New definition for MOHAVE implicitly acknowledged the change made to the Arizona - Nevada line on 5 May 1866. (Ariz. Terr. Laws 1871, 6th assy./ p. 87)

14 February 1873

MARICOPA gained from PIMA. (Ariz. Terr. Laws 1873, 7th assy./ p. 87)

01 February 1875

PINAL created by Arizona Territory from MARICOPA and PIMA; PIMA was divided into two parts. (Ariz. Terr. Laws 1875, 8th assy./ pp. 19-20)

31 January 1877

MARICOPA gained from YAVAPAI; PIMA gained a small area along the Gila River from MARICOPA. (Ariz. Terr. Laws 1877, 9th assy./ pp. 12-13)

09 February 1877

PINAL gained from PIMA. Area gained was the part of PIMA that had been separated from main body of the county on 1 February 1875. (Ariz. Terr. Laws 1877, 9th assy./ pp. 108-109)

14 February 1879

APACHE created by Arizona Territory from YAVAPAI. (Ariz. Terr. Laws 1879, 10th assy./ pp. 96-97)

01 February 1881

COCHISE created by Arizona Territory from PIMA. (Ariz. Terr. Laws 1881, 11th assy./ pp. 4-7)

08 February 1881

GILA created by Arizona Territory from MARICOPA and PINAL. (Ariz. Terr. Laws 1881, 11th assy./ pp. 14-17)

10 March 1881

GRAHAM created by Arizona Territory from APACHE and PIMA. (Ariz. Terr. Laws 1881, 11th assy./ pp. 155-157)

06 March 1883

MOHAVE exchanged with YAVAPAI. (Ariz. Terr. Laws 1883, 12th assy./ p. 171)

12 March 1885

GILA exchanged with GRAHAM. (Ariz. Terr. Laws 1885, 13th assy./ p. 215)

21 March 1889

GILA gained from YAVAPAI. (Ariz. Terr. Laws 1889, 15th assy./ pp. 49-52)

19 February 1891

COCONINO created by Arizona Territory from YAVAPAI. (Ariz. Terr. Laws 1891, 16th assy./ pp. 26-34)

19 March 1891

GILA gained from YAVAPAI. (Ariz. Terr. Laws 1891, 16th assy./ pp. 102-103)

21 March 1895

NAVAJO created by Arizona Territory from APACHE. (Ariz. Terr. Laws 1895, 18th assy./ pp. 96-105)

17 March 1897

Boundary between APACHE and GRAHAM clarified [no change]. (Ariz. Terr. Laws 1897, 19th assy./ p. 67)

15 March 1899

SANTA CRUZ created by Arizona Territory from PIMA. (Ariz. Terr. Laws 1899, 20th assy./ pp. 49-57)

10 March 1909

GREENLEE created by Arizona Territory from GRAHAM. (Ariz. Terr. Laws 1909, 25th assy./ pp. 43-56)

14 February 1912

Arizona admitted to the union with present boundaries and thirteen counties created by the territorial legislatures; Arizona Territory eliminated. (U.S. Stat., vol. 34, pt. 1, ch. 3335[1906]/pp. 267-285; U.S. Stat., vol. 36, pt. 1, ch. 310[1910]/pp. 557-579; U.S. Stat., vol. 37, pt. 1, res. 8[1911]/pp. 39-43; pt. 2[1912]/pp. 1728-1729)

11 February 1935

COCHISE boundaries redefined [no change]. (Ariz. Laws 1935, 12th reg. sess., ch. 7/p. 11)

24 March 1960

MOHAVE boundary with the state of Nevada was redefined as part of an interstate compact to account for changes in the course of the Colorado River. The adjusted state line apparently had a minor effect on the boundary between MOHAVE and CLARK (Nevada) [not mapped]. (Ariz. Laws 1960, 24th leg., 2d reg. sess., ch. 69/pp. 174-180)

02 April 1963

MOHAVE and YUMA boundaries with the state of California were redefined as part of an interstate compact to account for changes in the course of the Colorado River [not mapped]. (Ariz. Laws 1963, 25th leg., 1st reg. sess., ch. 77/ pp. 142-150)

14 March 1968

COCHISE gained from SANTA CRUZ when the boundary was redefined to run along the east line of range 18 east. (Ariz. Laws 1968, 28th leg., 1st reg. sess., ch. 82/ pp. 180-182)

02 May 1973

PIMA boundaries redefined [no change]. (Ariz. Laws 1973, 31st leg., 1st reg. sess., ch. 101/ pp. 596-597)

27 April 1983

LA PAZ created from YUMA. (Ariz. Laws 1983, 36th assy., ch. 291/pp. 1089-1094)