Thomaston is a city in and the county seat of Upson County, Georgia, United States. The population was 9,638 at the 2006 census. It is the principal city of and is included in the Thomaston, Georgia Micropolitan Statistical Area, which is included in the Atlanta - Sandy Springs - Gainesville - Alabama Combined Statistical Area.Thomaston is located on US Route 19 and State Route 3, which run north and south, and on State Routes 36 and 74, which run east and west.