Almost all of the county's western border is located in the Spring Creek sub-basin of the same ACF River Basin.

The southwestern portion of Decatur County, centered on Attapulgus, and bordered on the west by State Route 302, is located on the Lower Ochlockonee River sub-basin of the larger Ochlockonee River basin.

[6] As of the 2020 United States census, there were 29,367 people, 10,084 households, and 7,113 families residing in the county.

Abraham Baldwin Agricultural College has a satellite campus in Bainbridge.

Southern Regional Technical College has a satellite campus in Bainbridge serving the county.