San Antonio (ˌsæn_ænˈtoʊnioʊ ; Spanish for "Saint Anthony"), officially the City of San Antonio, is a city in and the county seat of Bexar County, Texas, United States. 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. It is the 12th-most populous city in North America, with 1,434,625 residents as of 2020. Founded as a Spanish mission and colonial outpost in 1718, the city in 1731 became the first chartered civil settlement in what is now present-day Texas. The area was then part of the Spanish Empire. From 1821 to 1836, it was part of the Mexican Republic. It is the oldest municipality in Texas, having celebrated its 300th anniversary on May 1, 2018. From 2000 to 2010, the city was the fastest growing of the top ten largest cities in the United States; it was the second in growth in that category from 1990 to 2000. San Antonio is the largest city of the San Antonio–New Braunfels metropolitan statistical area. Commonly called Greater San Antonio, the metropolitan area had a population of 2,601,788 based on the 2020 U.S. census estimates, making it the 24th-largest metropolitan area in the United States and third-largest in Texas. Straddling the regional divide between South and Central Texas, San Antonio anchors the southwestern corner of an urban megaregion colloquially known as the Texas Triangle. Downtown San Antonio and Downtown Austin are approximately apart, both falling along the Interstate 35 corridor. Some observers expect the two metropolitan regions to form a new metroplex similar to Dallas and Fort Worth. San Antonio was named by a 1691 Spanish expedition for the Portuguese priest Saint Anthony of Padua, whose feast day is June 13. The city contains five 18th-century Spanish frontier missions, including The Alamo and San Antonio Missions National Historical Park. Together these were designated as UNESCO World Heritage sites in 2015.