Where is Adams County?

12 Adams Counties in 12 states · 906,321 people (2025)

There are 12 counties named Adams County in the United States, in Colorado, Idaho, Illinois, Indiana, Iowa, Mississippi, Nebraska, North Dakota, Ohio, Pennsylvania, Washington and Wisconsin. The most populous is Adams County, Colorado (county seat: Brighton), with 554,668 people in 2025. 7 of them are named after John Adams, Founding Father, U.S. president from 1797 to 1801 (1735–1826).

Map of the United States showing where all 12 Adams Counties are, labeled by state
Every Adams County in the United States (red), labeled with its state. Boundaries: U.S. Census Bureau, 2025. Free to use with attribution (CC BY 4.0).

All 12 Adams Counties

Sorted by state. Each link opens the county's map.

StateCounty seatPopulation 2025Land area (sq mi)EstablishedNamed after
Adams County, ColoradoBrighton554,6681,1671902Alva Adams
Adams County, IdahoCouncil5,0131,3631911John Adams
Adams County, IllinoisQuincy64,2678551825John Quincy Adams
Adams County, IndianaDecatur36,6503391836John Quincy Adams
Adams County, IowaCorning3,6174231851John Adams
Adams County, MississippiNatchez30,0614621799John Adams
Adams County, NebraskaHastings31,0715631867John Adams
Adams County, North DakotaHettinger2,2759881907John Quincy Adams
Adams County, OhioWest Union27,8655841797John Adams
Adams County, PennsylvaniaGettysburg107,5945191800John Adams
Adams County, WashingtonRitzville21,4881,9251883John Adams
Adams County, WisconsinFriendship21,7526461848John Quincy Adams

Questions about Adams Counties

How many Adams Counties are there?

There are 12 Adams Counties in the United States, in Colorado, Idaho, Illinois, Indiana, Iowa, Mississippi, Nebraska, North Dakota, Ohio, Pennsylvania, Washington and Wisconsin.

Which Adams County is the largest?

By population, Adams County, Colorado (554,668 people in 2025). By land area, Adams County, Washington (1,925 sq mi).

Which Adams County is the oldest?

Adams County, Ohio, established in 1797. The newest is Adams County, Idaho (1911).

Why are there so many Adams Counties?

7 of the 12 are named after John Adams, Founding Father, U.S. president from 1797 to 1801 (1735–1826). Many counties took their names from the same founders, presidents and generals as new states were organized.

How do I find out which Adams County an address is in?

Open the county map of the state: it has a search box for cities, towns and ZIP codes. On a phone, the "what county am I in" tool on our sister site uses your location.

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Other common county names