Stephenville is a city in and the county seat of Erath County, Texas, United States. It is on the North Bosque River, which forms nearby. Founded in 1854, it is home to Tarleton State University. As of the 2020 census, the city's population was 20,847, and it is the principal city in the Stephenville Micropolitan Statistical Area. Stephenville is among several communities that call themselves the "Cowboy Capital of the World".