Thomaston is a town in Marengo County, Alabama, United States. At the 2020 census the population was 326, down from 417 at the 2010 census. Thomaston was platted in 1901 when the railroad was extended to that point. Thomaston was named for C. B. Thomas, a town promoter. A post office called Thomaston has been in operation since 1892. It was inc…Thomaston is a town in Marengo County, Alabama, United States. At the 2020 census the population was 326, down from 417 at the 2010 census. Thomaston was platted in 1901 when the railroad was extended to that point. Thomaston was named for C. B. Thomas, a town promoter. A post office called Thomaston has been in operation since 1892. It was incorporated on November 15, 1901.