DeKalb County is a county located in the U.S. state of Georgia. The population of the county was 691,893 at the 2010 census. Its county seat is the city of Decatur. It is bordered to the west by Fulton County and contains roughly 10% of the city of Atlanta. (The other 90% lies in Fulton County). DeKalb County is included in the five-county core of the Atlanta metropolitan statistical area.