San Antonio, formally the City of San Antonio, is the seventh-most populous city in the United States, the second-largest city in the Southern United States, and the second-most populous city in Texas, with 1,434,625 people in 2020. The city was established in 1718 as a Spanish mission and colonial outpost, and it was the first civil community to be founded in what is now the state of Texas in 1731. The territory was still a part of the Spanish Empire, and subsequently became a part of the Mexican Republic. It is the state's oldest town, which celebrated its 300th anniversary on May 1, 2018.
From 2000 to 2010, the city grew at the quickest rate among the top ten biggest cities in the United States, and it grew at the second fastest rate between 1990 and 2000. The city of San Antonio serves as the county seat of Bexar County, and it is the geographic centre of the San Antonio–New Braunfels metropolitan statistical region. According to the most recent U.S. census estimates, the Greater San Antonio metropolitan area has a population of 2,550,960 people, ranking it as the 24th-largest metropolitan area in the United States and the third-largest in Texas. San Antonio, located on the border of South and Central Texas, is the focal point of the Texas Triangle, an urban megaregion that spans the state's southern and central regions. The metropolitan regions of Greater San Antonio and Greater Austin are divided by roughly 80 miles (129 km) of Interstate 35. Both metropolitan areas are planned to merge to establish a new metroplex in the same vein as Dallas and Fort Worth.
The United States Armed Forces maintain a large number of sites in and around San Antonio; Fort Sam Houston is the only one located inside the city boundaries. Lackland Air Force Base, Randolph Air Force Base, Kelly Air Force Base, Camp Bullis, and Camp Stanley are all located outside the city limits. San Antonio is home to four Fortune 500 firms as well as the South Texas Medical Center, which is the primary medical research and treatment provider in the South Texas area.
San Antonio is also the most Hispanic-majority city in the United States, with 64 percent of the population being of Hispanic descent.