DeKalb County (/dəˈkæb/ də-KAB) is a county in the U.S. state of Georgia. As of the 2010 census, the population was 691,893, making it Georgia’s fourth-most populous county. Its county seat is Decatur.
DeKalb County is included in the Atlanta-Sandy Springs-Roswell, GA Metropolitan Statistical Area. It contains roughly 10% of the city of Atlanta (the other 90% lies in Fulton County
The county is crossed by the South River and numerous creeks, including Nancy Creek, Snapfinger Creek and two forks of Peachtree Creek. Peachtree Creek and Nancy Creek drain into the Chattahoochee River and eventually to the Gulf of Mexico. South River drains into the Ocmulgee River and ultimately into the Atlantic Ocean.
The southern two-thirds of DeKalb County, in a line from Druid Hills northeast to Tucker, is located in the Upper Ocmulgee River sub-basin of the Altamaha River basin, while the portion of the county north of that line is located in the Upper Chattahoochee River sub-basin of the ACF River Basin (Apalachicola-Chattahoochee-Flint River Basin).
Stone Mountain lies near the eastern border of the county. Soapstone Ridge, parallel to the southern border, was heavily quarried between 1400 and 100 B.C. and objects made from the soapstone have been found as far away as the Great Lakes.