Erath County is a county located in the U.S. state of Texas. According to the United States Census bureau its population was 42,545 in 2020. The county seat is Stephenville. The county is named for George Bernard Erath, an early surveyor and a soldier at the Battle of San Jacinto. Erath County is included in the Stephenville, Texas, Micropolitan Statistical Area. Erath County is the location of two of North America's largest renewable natural gas plants.