Sierra Blanca is a census-designated place (CDP) in and the county seat of Hudspeth County, Texas, United States. The population was 533 at the 2000 census. The town, founded in 1881 at the completion point of a long-sought southern transcontinental railway, was named for nearby Sierra Blanca Mountain, which was named for the white poppies which grew on it (sierra blanca is Spanish for white mountain).