Mercedes is a city in Hidalgo County, Texas, United States. The population was 15,570 at the 2010 United States Census. It is part of the McAllen–Edinburg–Mission and Reynosa–McAllen metropolitan areas.GeographyMercedes is located at .According to the United States Census Bureau, the city has a total area of 8.6sqmi, of which 8.6sqmi is land and 0.1sqmi is water.HistoryMercedes is known as "The Queen City of the Valley" or "La Reina del Valle". The city of Mercedes was founded September 15, 1907, by the American Rio Grande Land & Irrigation Company, and was incorporated March 8, 1909. It is one of the oldest towns in the Rio Grande Valley, and the city celebrated its centennial in 2007.The city was located in Capisallo Pasture, part of Capisallo Ranch owned by Jim Welles. This location was known as the Pear Orchard because of the vast numbers of prickly pear cactus growing there at that time.Some sources state that the original name given to the city was Diaz in honor of Porfirio Diaz, then president of Mexico. Later it was renamed Mercedes Diaz in honor of the president's wife and from that, Mercedes became the Queen City. This story, however, is historically inaccurate, given that neither of Diaz's two wives were named Mercedes.General Zachary Taylor's headquarters was to the southeast of Mercedes near the river. There the old Rabb Ranch was famous for its stagecoach stop and riverboat landing for the riverboats that plied the Rio Grande carrying supplies to the settlements and military installations.