Where is DeKalb County?

6 DeKalb Counties in 6 states · 1 million people (2025)

There are 6 counties named DeKalb County in the United States, in Alabama, Georgia, Illinois, Indiana, Missouri and Tennessee. The most populous is DeKalb County, Georgia (county seat: Decatur), with 774,394 people in 2025. 6 of them are named after Johann de Kalb, American general (1721-1780).

All 6 DeKalb Counties

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

State	County seat	Population 2025	Land area (sq mi)	Established	Named after
DeKalb County, Alabama	Fort Payne	74,085	777	1836	Johann de Kalb
DeKalb County, Georgia	Decatur	774,394	268	1822	Johann de Kalb
DeKalb County, Illinois	Sycamore	101,835	631	1837	Johann de Kalb
DeKalb County, Indiana	Auburn	44,535	363	1835	Johann de Kalb
DeKalb County, Missouri	Maysville	9,795	421	1843	Johann de Kalb
DeKalb County, Tennessee	Smithville	21,873	304	1837	Johann de Kalb

Questions about DeKalb Counties

How many DeKalb Counties are there?

There are 6 DeKalb Counties in the United States, in Alabama, Georgia, Illinois, Indiana, Missouri and Tennessee.

Which DeKalb County is the largest?

By population, DeKalb County, Georgia (774,394 people in 2025). By land area, DeKalb County, Alabama (777 sq mi).

Which DeKalb County is the oldest?

DeKalb County, Georgia, established in 1822. The newest is DeKalb County, Missouri (1843).

Why are there so many DeKalb Counties?

6 of the 6 are named after Johann de Kalb, American general (1721-1780). Many counties took their names from the same founders, presidents and generals as new states were organized.

How do I find out which DeKalb 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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