Mercedes is located in Hidalgo County in South Texas in a geographic area called the Lower Rio Grande Valley, which is really a river delta at the mouth of the Rio Grande River first inhabited by Coahuiltecans. Spanish colonists arrived in this area in 1749 to establish ranching communities. In 1905, the American Rio Grande Land and Irrigation Company purchased land in the Llano Grande Spanish land grant, built Mercedes as a showcase headquarters, constructed the largest irrigation system then known, and proceeded to develop the area through commercialized agriculture. Home of notable author Dr. Rolando Hinojosa-Smith, G.I. Forum founder Dr. Hector P. Garcia, Olympic athlete Billy Gene Pemelton, US congressman Ruben Hinojosa, and the Rio Grande Valley Livestock Show, Mercedes continues to attract many visitors who seek the mild climate and warm hospitality of the town."