Santa Maria del Rio is one of the 58 municipalities that make up the Mexican state of San Luis Potosi. The municipality is located in the southern part of the state, approximately 48 kilometers east of the city of San Luis Potosi. Santa Maria del Rio has a land area of 1,655 square kilometers, with 37,290 inhabitants As of 2005, 12,000 of whom live in the town of Santa Maria del Rio.