County

Counties and Equivalent Entities are primary legal divisions of most states are termed "counties." In Louisiana, these divisions are known as "parishes." In Alaska, the equivalent entities are the organized boroughs, city and boroughs, and municipalities, and for the unorganized area, census areas. The latter are delineated cooperatively for statistical purposes by the State of Alaska and the Census Bureau. In four states (Maryland, Missouri, Nevada, and Virginia), there are one or more incorporated places that are independent of any county organization and thus constitute primary divisions of their states. These incorporated places are known as independent cities and are treated as county equivalent entities for purposes of data presentation. The District of Columbia and Guam have no primary divisions and each area is considered a county equivalent entity for purposes of data presentation. The Census Bureau treats
the following entities as equivalents of counties for purposes of data presentation: municipios in Puerto Rico, districts and islands in America Samoa, municipalities in the Commonwealth of the Northern Mariana Islands, and islands in the U.S. Virgin Islands. Each county or statistically equivalent entity is assigned a three-digit Federal Information Processing Series (FIPS) code that is unique within a state, as well as an eight-digit National Standard (ANSI) code.

Since Census 2000, there have been several changes to the universe of county or equivalent entities. In Colorado, Broomfield County was created from parts of Adams, Boulder, Jefferson, and Weld Counties. The independent city of Clifton Forge, Virginia, changed its status to become Clifton Forge town and is now part of Alleghany County, Virginia. In Alaska: 1) Skagway Municipality was created from part of Skagway-Hoonah-Angoon Census Area and the former Skagway-Hoonah-Angoon Census Area was renamed Hoonah-Angoon Census Area, 2) Wrangell City and Borough was created from part of Wrangell-Petersburg Census Area and the former Wrangell-Petersburg Census Area was renamed Petersburg Census Area, and 3) Ketchikan Gateway annexed the area of Outer Ketchikan from the Prince of Wales-Outer Ketchikan Census Area, which subsequently was renamed Prince of Wales-Hyder Census Area. The 2010 TIGER/Line Shapefiles are based on available governmental unit boundaries of the counties and equivalent entities as of January 1, 2010.;