Southborough is a town in Worcester County, Massachusetts, United States. It incorporates the villages of Cordaville, Fayville, and Southville. Its name is often informally shortened to Southboro, a usage seen on many area signs and maps. At the 2020 census, its population was 10,450 in 3,542 households. As of 2021, 43% of land use was residential, with 35% open space, including one-tenth of the town's area that is flooded by the Sudbury Reservoir.