The United States acquired the area of Idaho through a treaty with Great Britain in 1846.  Idaho Territory was organized from parts of Dakota, Nebraska, and Washington territories on March 3, 1863, and included parts of present-day Montana and Wyoming. Its area was reduced in 1864 by the organization of Montana Territory and again in 1868 by the organization of Wyoming Territory, to generally the same boundary as the present state. Idaho was admitted to the Union on July 3, 1890, as the 43^rd state.

Census data for Idaho are available beginning with the 1870 census. The portion of Yellowstone National Park in Idaho was probably enumerated as part of Wyoming from 1880 to 1910. The area was shown as a separate county equivalent in the census reports for Idaho from 1920 to 1960. The portion of the park in Idaho was legally added to Fremont County before the 1970 census.

Data for the legally established state of Idaho are available beginning with the 1900 census.  The census day for the 1890 census was June 2, 1890.

American Indian Areas

Idaho has five federally recognized American Indian reservations; two with associated off-reservation trust land.

Metropolitan And Micropolitan Statistical Areas And Related Statistical Areas

Idaho has six metropolitan statistical areas, eight micropolitan statistical areas, and one combined statistical area.

Counties

There are 44 counties in Idaho.  All counties are functioning governmental units, each governed by a board of commissioners.

County Subdivisions

There are 170 county subdivisions in Idaho. 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 Idaho for the 1960 census.  Prior to 1960, the minor civil divisions used for the census included election precincts, land-survey townships, and Indian reservations.

Places

Idaho has 227 places; 201 incorporated places and 26 census designated places. The incorporated places are all cities.  Lost River city is governmentally inactive. 

Census Tracts/Block Groups/Blocks

There are 298 census tracts, 963 block groups, and 149,842 census blocks in Idaho.

Congressional Districts

For the 111^th Congress (January 2009-January 2011), Idaho had two congressional districts.  For the 113^th Congress (January 2013-January 2015), Idaho continues to have two congressional districts as a result of reapportionment based on the 2010 Census.

School Districts

Idaho has 115 unified school districts.

State Legislative Districts

There are 35 state senate districts and 35 state house districts in Idaho.

Urban Areas

Idaho has 43 urban areas; 6 urbanized areas and 37 urban clusters.

Zip Code Tabulation Areas

There are 285 ZIP Code tabulation areas (ZCTAs) in Idaho.

Other Information Of General Geographic Interest

A portion of Yellowstone National Park is located in Fremont County. The remainder of the park is located in Montana and Wyoming. Prior to the 1970 census, Yellowstone National Park was an entity separate from any county government.

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