The area of the District of Columbia was part of the original territory of the United States. The District of Columbia was formed from territory ceded by Maryland and Virginia in 1788, and was established in accordance with Acts of Congress passed in 1790 and 1791. Its boundary, a square ten miles on a side with vertices at the cardinal points to resemble a diamond, was established on March 30, 1791, and included all of the territory within present-day Arlington County, Virginia, and part of Alexandria city, Virginia. The portion south of the Potomac River was retroceded to Virginia in 1846.

Census data for the District of Columbia are available beginning with the 1800 census. The population shown for the District of Columbia from 1800 to 1840 does not include the portion of Virginia legally included in the district at the time of those censuses. The population of the District of Columbia as legally existent in those censuses is: 43,712 in 1840; 39,834 in 1830; 33,039 in 1820; 24,023 in 1810; and 14,093 in 1800. Congress abolished the original county (Washington County) and incorporated places (Georgetown and Washington cities) in the District of Columbia in 1871, but later reestablished the city of Washington. The Census Bureau continued to recognize the boundaries of the previously existing areas for the 1880 and 1890 censuses. Congress has treated the District of Columbia as coextensive with Washington city since 1895.

METROPOLITAN AND MICROPOLITAN STATISTICAL AREAS AND RELATED STATISTICAL AREAS

The District of Columbia is part of one metropolitan statistical area, one metropolitan division, and one combined statistical area.

COUNTIES

The District of Columbia does not contain any counties, but it is considered a county equivalent for the purposes of data presentation.

COUNTY SUBDIVISIONS

There are no county subdivisions in the District of Columbia, but it is considered a county subdivision equivalent for the purposes of data presentation.

PLACES

The District of Columbia has one city, Washington, which is coextensive with the District of Columbia.  Washington city governmentally consolidated with the District of Columbia in 1874, which is a functioning government at the equivalent of the state level.

CENSUS TRACTS/BLOCK GROUPS/BLOCKS

The District of Columbia has 179 census tracts, 450 block groups, and 6,507 census blocks.

CONGRESSIONAL DISTRICTS

The District of Columbia has a delegate district (at large), with one non-voting delegate.

SCHOOL DISTRICTS

There is one unified school district in the District of Columbia.

STATE LEGISLATIVE DISTRICTS

There are eight wards in the District of Columbia which are represented by the Census Bureau as state legislative districts – upper chamber because the District of Columbia has a single council government.

URBAN AREAS

District of Columbia has 1 urban area; 1 urbanized area and 0 urban clusters.

ZIP CODE TABULATION AREAS

There are 53 ZIP Code tabulation areas (ZCTAs) in the District of Columbia.

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.