San Antonio ( SAN an-TOH-nee-oh; Spanish for "Saint Anthony"), officially the City of San Antonio, is a city in Bexar County, Texas. 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. 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. The city of San Antonio serves as the seat of Bexar County; San Antonio is the center 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 80 miles (130 km) 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. Other notable attractions include the River Walk, the Tower of the Americas, SeaWorld San Antonio, the Alamo Bowl, and Marriage Island. Commercial entertainment includes Six Flags Fiesta Texas and Morgan's Wonderland amusement parks. According to the San Antonio Convention and Visitors Bureau, the city is visited by about 32 million tourists a year. It is home to the five-time National Basketball Association (NBA) champion San Antonio Spurs. It hosts the annual San Antonio Stock Show & Rodeo, one of the largest such events in the U.S.

The U.S. Armed Forces have numerous facilities in and around San Antonio; Fort Sam Houston, which has Brooke Army Medical Center within it, is the only one within the city limits. Lackland Air Force Base, Randolph Air Force Base, Kelly Air Force Base, Camp Bullis, and Camp Stanley are outside the city limits. San Antonio is home to four Fortune 500 companies and the South Texas Medical Center, the only medical research and care provider in the South Texas region.

San Antonio is also the largest majority-Hispanic city in the United States, with 64% of its population being Hispanic.