In 45 of the 50 states of the United States, the county is used for the level of local government immediately below the state itself. Louisiana uses parishes, and Alaska uses boroughs. In Connecticut, Massachusetts, and Rhode Island, some or all counties within states have no governments of their own; the counties continue to exist as legal entities, however, and are used by states for some administrative functions and by the United States Census bureau for statistical analysis. There are 3,242 counties and county equivalent administrative units in total, including the District of Columbia and 100 county-equivalents in the U.S. territories.

The North Slope Borough is the northernmost borough in the US state of Alaska and thus, the northernmost county or equivalent of the United States as a whole. As of the 2020 census, the population was 11,031. The borough seat and largest city, comprising nearly 1/2 of the borough’s population, is Utqiaġvik, the northernmost settlement in the United States.