Decatur is a city in, and county seat of, DeKalb County, Georgia, United States. With a population of 19,335 in the 2010 census, the city is sometimes assumed to be larger since multiple zip codes in unincorporated DeKalb County bear the Decatur name. It is an intown suburb of Atlanta and part of the Atlanta Metropolitan Area, and its public transportation is served by three MARTA rail stations.