Presidio County is a county located in the U.S. state of Texas. As of the 2010 census, its population was 7,818. Its county seat is Marfa. The county was created in 1850 and later organized in 1875. Presidio County (K-5 in Texas topological index of counties) is in the Trans-Pecos region of West Texas and is named for the ancient border settlement of Presidio del Norte. It is on the Rio Grande, which forms the Mexican border.