Stephenville is a city in and the county seat of Erath County, Texas, United States. It sits on the North Bosque River, which rises nearby. Founded in 1854, it is home to Tarleton State University. Stephenville's population was 20,847 as of the 2020 census, 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".