Dorchester is a city in Grayson County, Texas, United States. The population was 69 at the 2020 census, significantly down from 148 a…Dorchester is a city in Grayson County, Texas, United States. The population was 69 at the 2020 census, significantly down from 148 at the 2010 census. It is part of the Sherman–Denison Metropolitan Statistical Area.