Duluth, GA. Online Offers. Duluth is a city in Gwinnett County, Georgia, and a suburb of Atlanta, and is an increasingly more affluent and developed suburb of Atlanta. Unincorporated portions of Forsyth County also have Duluth as a mailing address, though this area is outside city limits. Much of the adjacent city of Johns Creek (incorporated in 2006) uses one of the Duluth ZIP codes. The population of Duluth was 26,668 at the 2010 census, making it the second most populous city in Gwinnett County, behind Lawrenceville. Duluth is a suburb of Atlanta, close to Interstate 85.