Overview of the territorial administrative structure of the United States. Below the federal level, states and counties are the major legally defined political and administrative units of the United States. As such, they serve as the primary geographic units for which data are collected and reported. For instance, the U.S. Census Bureau provides statistics for these entities in every decennial census of population and housing, in every census of agriculture and governments, and in all the economic censuses. It tabulates data for States and counties in post-census estimates and sometimes in its various inter-census sample surveys and projections as well.

In certain circumstances, the Census Bureau classifies entities as the statistical equivalents of States or of counties for data presentation purposes. Both States and counties (including their equivalents) provide complete coverage of all land area and population in the United States at their geographic levels. 

Federal and state-level data. The United States comprises the 50 States and the District of Columbia. For
data presentation purposes, the Census Bureau treats the District of Columbia as the statistical equivalent of a State.

Significant Features generally does not present data for territories under U.S. sovereignty or jurisdiction, including American Samoa, Guam, the Northern Mariana Islands, Palau, Puerto Rico, and the Virgin Islands of the United States.

Counties and county-equivalent jurisdictions. Counties (and county equivalents) are generally the primary territorial-administrative subdivision of their respective state, and therefore, the second-level administrative subdivision of the United States.

The term “county” is used in 48 U.S. states, while Louisiana and Alaska have functionally equivalent subdivisions called parishes and boroughs, respectively. There are currently 3,142 counties and county equivalents in the United States. Counties are generally—but not always—governed by their own local government. For 2017, the Census of Governments indicates that there are 3,031 county governments. (Table 1.1.1)

For instance, whereas New York State is subdivided into 62 counties, the five counties (or boroughs) that comprise New York City do not have separate county governments.  In Rhode Island, Connecticut and parts of Massachusetts, county governments have been abolished but the entities remain for administrative or statistical purposes. Alaska’s Unorganized Borough is divided into 10 census areas that are statistically equivalent to counties. In addition, Maryland (Baltimore City), Montana (part of Yellowstone National Park), Nevada (Carson City) and Virginia (41 independent cities) contain jurisdictions that are considered county equivalents by the U.S. Census Bureau for geographic and statistical classification purposes. (It should be noted that the Census of Governments uses its own considerations in classifying local governments; therefore, the governing body of a county equivalent jurisdiction is not necessarily classified as a county). 

Delineation of metropolitan (and micropolitan) areas. The nationwide geographic framework provided by counties makes it possible to combine counties and statistically equivalent entities into larger statistical units, which may encompass an entire State or selected parts of several States. One of the best known examples of county combinations are metropolitan statistical areas.

A metropolitan or micropolitan statistical area’s geographic composition, or list of geographic components at a particular point in time, is referred to as its “delineation." Metropolitan and micropolitan statistical areas are delineated by the U.S. Office of Management and Budget (OMB) and are the result of the application of published standards to Census Bureau data.

State and local government FIPS codes. In order to facilitate matching state and local-level data, Significant Features generally identifies state and local governments using their Federal Informational Processing Standard (FIPS) code.

Each state is identified by a two-digit code (e.g., Alabama – 01; Alaska – 02; and son on), while counties or county-equivalent areas within each state are identified by a three-digit code. As a result, each county in the country can be identified by a five-digit FIPS code (e.g., Autauga County, Alabama – 01001; Baldwin County, Alabama – 01003; etc.).

In addition, additional FIPS location codes are available for County Subdivisions; Places; and Consolidated Cities.