Stephenville is a city in and the county seat of Erath County, Texas, United States. It has a population of about 21.000. It was named after the founder John M. Stephen, who settled there in 1854, and donated the land for the townsite laid out by George B. Erath when the county was organized in 1856. The median income for a family living in Stephenville is about $52.000. It is home to Tarleton State University. Stephenville is among several communities that call themselves the "Cowboy Capital of the World".