South Texas is a region of the U.S. state of Texas that lies roughly south of—and includes—San Antonio. The southern and western boundary is the Rio Grande, and to the east it is the Gulf of Mexico. The population of this region is about 4.96 million according to the 2017 census estimates. The southern portion of this region is often referred to as the Rio Grande Valley. The eastern portion along the Gulf of Mexico is also referred to as the Coastal Bend.

San Antonio, officially the City of San Antonio, is a city in the U.S. state of Texas and the most populous city in Greater San Antonio, the third-largest metropolitan area in Texas and the 24th-largest metropolitan area in the United States at 2.6 million people in 2020. It is the most populous city in and seat of Bexar County. The city is the seventh-most populous in the United States, the second-largest in the Southern United States, and the second-most populous in Texas after Houston.