City of Decatur 509 N McDonough St, Decatur, GA30030 City of Decatur, which sits about six miles east of downtown Atlanta, was founded in 1823 and is named for 19th century…More U.S. Naval hero Stephen Decatur. It's the second oldest municipality in the metro Atlanta area and is the county seat of DeKalb government. The city has 18,000 residents and 8,000 households.The Mayor of the City of Decatur is Bill Floyd. Mayor Pro Tem is Jim Baskett.