The United States acquired most of the area of Arizona from Mexico in 1848. The United States acquired additional area, comprising the southern part of Arizona, from Mexico in 1853 as part of the Gadsden Purchase. Arizona Territory was organized from the western part of New Mexico Territory on February 24, 1863. Part of Arizona Territory north and west of the Colorado River was added to the state of Nevada in 1866, resulting in generally the same boundary as the present state of Arizona.

Although the territory had not yet been legally established, census data are available for Arizona beginning with the 1860 census. For an explanation of the revision to the 1860 population of Arizona, see Richard L. Forstall, Population of States and Counties of the United States: 1790-1990, Washington, DC: U.S. Government Printing Office, 1996, page 14.

Data for the legally established state of Arizona are available beginning with the 1920 census.

AMERICAN INDIAN AREAS

Arizona has 21 federally recognized American Indian reservations; 4 with associated off-reservation trust lands in the state.

METROPOLITAN AND MICROPOLITAN STATISTICAL AREAS AND RELATED STATISTICAL AREAS

Arizona has six metropolitan statistical areas and five micropolitan statistical areas.

COUNTIES

There are 15 counties in Arizona.  Each county is governed by a board of supervisors.

COUNTY SUBDIVISIONS

There are 80 county subdivisions in Arizona.  They are all census county divisions (CCDs), which are delineated for statistical purposes, have no legal function, and are not governmental units.  CCDs were first established in Arizona for the 1960 census.  Prior to 1960, the minor civil divisions used in the census include supervisorial districts, election precincts, justice precincts, school districts, land-survey townships, and Indian reservations.

PLACES

Arizona has 451 places; 90 incorporated places and 361 census designated places (CDPs).  The incorporated places consist of 45 cities and 45 towns.  The minimum population threshold required for incorporation is 1,500. 

CENSUS TRACTS/BLOCK GROUPS/BLOCKS

Arizona has 1,526 tracts, 4,178 block groups, and 241,666 blocks.

CONGRESSIONAL DISTRICTS

For the 111^th Congress (January 2009-January 2011), Arizona had eight congressional districts.  For the 113^th Congress (January 2013-January 2015), Arizona has nine congressional districts as a result of reapportionment based on the 2010 Census.

SCHOOL DISTRICTS

Arizona has 104 elementary school districts, 15 secondary school districts, and 99 unified school districts.

STATE LEGISLATIVE DISTRICTS

There are 30 state senate districts and 30 state house districts in Arizona.

URBAN AREAS

Arizona has 69 urban areas; 9 urbanized areas and 60 urban clusters.

ZIP CODE TABULATION AREAS

There are 408 ZIP Code tabulation areas (ZCTAs) in Arizona.

¹  Source:  U.S. Department of Commerce, Bureau of the Census, Fourteenth Census of the United States, 1923
²  Source:  U.S. Census Bureau, recomputation for historical county level data which relied upon aggregate county level population data with an estimated county centroid resulting in a possible error of up to one mile.
³  Source:  U.S. Department of Commerce, Bureau of the Census, Centers of Population for States and Counties, 1974
⁴  Source:  U.S. Census Bureau, Geography Division, recomputation from archived national block group/enumeration area data resulting in a possible error of up to 1,000 feet.
⁵  Source:  U.S. Census Bureau, Geography Division, recomputation from archived national block group data resulting in a possible error of up to 1,000 feet.
⁶  Source:  U.S. Census Bureau, computation from national block-level data