Where is Williamson County?

3 Williamson Counties in 3 states · 1.1 million people (2025)

There are 3 counties named Williamson County in the United States, in Illinois, Tennessee and Texas. The most populous is Williamson County, Texas (county seat: Georgetown), with 752,827 people in 2025. 2 of them are named after Hugh Williamson, American politician (1735-1819).

Map of the United States showing where all 3 Williamson Counties are, labeled by state
Every Williamson 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 3 Williamson Counties

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

StateCounty seatPopulation 2025Land area (sq mi)EstablishedNamed after
Williamson County, IllinoisMarion67,2254201839Hugh Williamson
Williamson County, TennesseeFranklin272,0615831799Hugh Williamson
Williamson County, TexasGeorgetown752,8271,1161848Robert McAlpin Williamson

Questions about Williamson Counties

How many Williamson Counties are there?

There are 3 Williamson Counties in the United States, in Illinois, Tennessee and Texas.

Which Williamson County is the largest?

By population, Williamson County, Texas (752,827 people in 2025). By land area, Williamson County, Texas (1,116 sq mi).

Which Williamson County is the oldest?

Williamson County, Tennessee, established in 1799. The newest is Williamson County, Texas (1848).

Why are there so many Williamson Counties?

2 of the 3 are named after Hugh Williamson, American politician (1735-1819). Many counties took their names from the same founders, presidents and generals as new states were organized.

How do I find out which Williamson 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.

What county am I in? →

Other common county names