Where is Jefferson County?

25 Jefferson Counties in 25 states · 3.3 million people (2025)

There are 25 counties named Jefferson County in the United States, in Alabama, Arkansas, Colorado, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Mississippi, Missouri, Montana, Nebraska, New York, Ohio, Oklahoma, Oregon, Pennsylvania, Tennessee, Texas, Washington, West Virginia and Wisconsin. The most populous is Jefferson County, Kentucky (county seat: Louisville), with 795,222 people in 2025. 24 of them are named after Thomas Jefferson, Founding Father, U.S. president from 1801 to 1809 (1743–1826).

Map of the United States showing where all 25 Jefferson Counties are, labeled by state
Every Jefferson 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 25 Jefferson Counties

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

StateCounty seatPopulation 2025Land area (sq mi)EstablishedNamed after
Jefferson County, AlabamaBirmingham665,7421,1121819Thomas Jefferson
Jefferson County, ArkansasPine Bluff62,9878721829Thomas Jefferson
Jefferson County, ColoradoGolden580,4517641861Thomas Jefferson
Jefferson County, FloridaMonticello16,0075981827Thomas Jefferson
Jefferson County, GeorgiaLouisville15,0115271796Thomas Jefferson
Jefferson County, IdahoRigby35,2971,0941913Thomas Jefferson
Jefferson County, IllinoisMount Vernon36,1475711819Thomas Jefferson
Jefferson County, IndianaMadison33,2793611811Thomas Jefferson
Jefferson County, IowaFairfield15,2914361839Thomas Jefferson
Jefferson County, KansasOskaloosa18,2965331855Thomas Jefferson
Jefferson County, KentuckyLouisville795,2223811780Thomas Jefferson
Jefferson County, MississippiFayette6,8255201799Thomas Jefferson
Jefferson County, MissouriHillsboro233,1326561818Thomas Jefferson
Jefferson County, MontanaBoulder13,3291,6571865Thomas Jefferson
Jefferson County, NebraskaFairbury7,0705701856Thomas Jefferson
Jefferson County, New YorkWatertown111,5401,2681805Thomas Jefferson
Jefferson County, OhioSteubenville63,5974081797Thomas Jefferson
Jefferson County, OklahomaWaurika5,4317591907Thomas Jefferson
Jefferson County, OregonMadras25,7401,7821914Mount Jefferson
Jefferson County, PennsylvaniaBrookville43,2556531804Thomas Jefferson
Jefferson County, TennesseeDandridge60,0242751792Thomas Jefferson
Jefferson County, TexasBeaumont254,3218771836Thomas Jefferson
Jefferson County, WashingtonPort Townsend33,9701,8041852Thomas Jefferson
Jefferson County, West VirginiaCharles Town63,1022091801Thomas Jefferson
Jefferson County, WisconsinJefferson86,5055571836Thomas Jefferson

Questions about Jefferson Counties

How many Jefferson Counties are there?

There are 25 Jefferson Counties in the United States, in Alabama, Arkansas, Colorado, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Mississippi, Missouri, Montana, Nebraska, New York, Ohio, Oklahoma, Oregon, Pennsylvania, Tennessee, Texas, Washington, West Virginia and Wisconsin.

Which Jefferson County is the largest?

By population, Jefferson County, Kentucky (795,222 people in 2025). By land area, Jefferson County, Washington (1,804 sq mi).

Which Jefferson County is the oldest?

Jefferson County, Kentucky, established in 1780. The newest is Jefferson County, Oregon (1914).

Why are there so many Jefferson Counties?

24 of the 25 are named after Thomas Jefferson, Founding Father, U.S. president from 1801 to 1809 (1743–1826). Many counties took their names from the same founders, presidents and generals as new states were organized.

How do I find out which Jefferson 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