Sierra Blanca is a census-designated place in and the county seat of Hudspeth County, Texas, in the United States. The town is part of the Trans-Pecos region of far western Texas. The town is located northeast from the Mexican border and is located within the Mountain Time Zone. As of the 2010 census, the population was 553.The town was founded in 1881 at the completion point of a long-sought southern transcontinental railway. Sierra Blanca has served as the junction of the Southern Pacific and Missouri Pacific railroads. Hudspeth County was formed in 1917 from El Paso County. Sierra Blanca was named the county seat, and has the only adobe courthouse in the state of Texas.The town continues to accommodate travelers along interstate 10 between Van Horn and El Paso which is the main route that connects Texas from west to east. The town was named for the nearby Sierra Blanca Mountains, which was named for the white poppies which grew on it.