Terrell County is a county in the U.S. state of Texas. As of the 2020 census, its population was 760, making it the seventh-least populous county in Texas, and the 37th-least populous county in the nation. Its county seat is the census-designated place of Sanderson; no incorporated municipalities are in the county. The county was named for Alexander W. Terrell, a Texas state senator. Terrell County is one of the nine counties in the Trans-Pecos region of West Texas.