Glossary of county terms

The terms that come up on this site, defined plainly. Where a term is genuinely ambiguous, the entry says so rather than picking one meaning.

Last updated 30 August 2026.

These are definitions rather than articles, and they are collected here on purpose. Search results for "what is a county seat" and similar are answered directly on the results page by dictionary sources, so a separate page competing for each one would add nothing. The explainers cover the questions that genuinely need more than a paragraph.

County: The primary administrative division below the state, used by forty-eight states. Typically responsible for courts, property records, assessment and tax collection, elections, vital records, the sheriff and rural roads. Louisiana calls them parishes and Alaska has boroughs instead. The longer version.
County-equivalent: The Census Bureau's category for anything occupying the same position in the geographic hierarchy as a county, whatever it is called locally. There are 3,144 across the fifty states and the District of Columbia, of which 2,999 are legally called counties.
County seat: The place where a county's government sits, in practice the courthouse and the offices of the clerk, recorder, assessor and sheriff. Not universal: 21 US county-equivalents have no seat because they have no county government, and 54 are their own seat because the city and the county-equivalent are the same government. More.
Parish: Louisiana's word for a county. Functionally identical: same position in the hierarchy, same kinds of responsibility. The name descends from Spanish colonial ecclesiastical districts and was written into law in 1807. There are 64. Why.
Borough: Alaska's organised county-equivalent. Alaska has no counties at all. It has 13 boroughs, 4 cities and boroughs, 2 municipalities, and 11 census areas. Why.
Census area: A Census Bureau statistical subdivision of Alaska's Unorganized Borough. There are 11. They are not governments, have never been governments, and have no seat or elected officials. They exist so the Bureau has a geography to publish statistics against.
Planning region: Connecticut's county-equivalent since the 2022 Census vintage. Nine of them replaced the eight former counties. They are groups of towns and are not the same shape as the counties they replaced, so no county-to-region crosswalk exists. What happened.
Independent city: A city belonging to no county, treated as a county-equivalent in its own right. There are 40: 38 in Virginia, plus Baltimore city and St. Louis city. Carson City, Nevada is a similar case with no type word in its name at all. More.
Consolidated city-county: A single government serving both a city and the county-equivalent it occupies. The District of Columbia, Honolulu, San Francisco, Denver, Philadelphia, Nashville and the five New York City boroughs are among them. These entities are their own seat.
FIPS code: A five-digit county identifier: two digits for the state, three for the county, zero-padded. Los Angeles County is 06037. It must be stored as text, because 01001becomes 1001 as a number and breaks every lookup. Why codes sometimes change.
GEOID: The Census Bureau's identifier for a geography. For counties it is the same five digits as the FIPS code. GEOIDFQ is the fully qualified form used on data.census.gov, prefixed0500000US.
COUNTYNS: An eight-digit ANSI identifier from the Geographic Names Information System. Unlike the FIPS code it survives a rename, which makes it the durable key when tracking a county across vintages.
LSAD: Legal or Statistical Area Description. The Census Bureau's code for what kind of entity something is: county, parish, borough, census area, city, municipality, planning region. Nine of them are in use across county-equivalents.
Land area and water area: Reported separately. Land area excludes inland, coastal and territorial water. Rankings on this site use land area, because total area makes coastal counties look larger in a way that does not reflect anything a reader means by size.
Population density: People per square mile of land. The Census Bureau does not publish it for counties; it is computed. On this site it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, and every page showing a density says so.
Vintage: Which edition of a dataset a figure came from. Vintage 2025 population estimates were released in March 2026 and give figures as of 1 July 2025. Two figures from different vintages are not comparable, which is the single most common way county statistics get misreported. More.
Estimates base: The 2020 starting point for the annual estimate series. It is not identical to the published 2020 Census count: it incorporates Count Question Resolution corrections and boundary updates. Quoting it as "the 2020 Census" is wrong, and common.
American Community Survey: A continuous sample survey, separate from the decennial count. One-year estimates are published only for areas of 65,000 or more, so most counties have only five-year estimates. Income, home value, age and housing figures on this site come from the five-year series.
Margin of error: The uncertainty around a survey estimate. It widens as the population being sampled shrinks, and in the smallest counties it can approach or exceed the estimate itself. County pages for places under 5,000 people carry a warning about this.
Adjacency: Which counties share a border. The Census Bureau publishes this, and since the 2025 file it also publishes the length of each shared border, which is where the border lengths on county pages come from.
Cartographic boundary file: A generalised boundary dataset published by the Census Bureau for mapping, clipped to the shoreline. Distinct from TIGER/Line, which is the unsimplified legal geometry and extends into territorial water. This site uses the cartographic files. Why.