Before Spaniards arrived in Mexico in 1519, Pachal Indians lived in this area. Alonso de Leon was the first explorer here in 1690, searching for Fort St. Louis founded by La Salle. The Upper Presidio Road, an artery of travel from Saltillo, Mexico, to East Texas, crossed the Frio River and became a King's Highway in 1720. Frio Town, the first county seat, stood on that road, over which Santa Anna marched in 1836 to destroy the defenders of the Alamo. The county took its name from the Frio River, using a Spanish word meaning "cold," and the county seat moved to Pearsall in 1883. The jail built in 1884 is the oldest building in town.