San Antonio, officially the City of San Antonio, is the seventh most populous city in the United States and the second most populous city in both Texas and the Southern United States. Founded as a Spanish mission and colonial outpost in 1718, the city became the first chartered civil settlement in Texas in 1731, making it the state's oldest municipality. The city's deep history is contrasted with its rapid growth: it was the fastest-growing of the top ten largest cities in the United States from 2000 to 2010, and the second from 1990 to 2000. 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".San Antonio serves as the seat of Bexar County. Recent annexations have extended the city's boundaries into Medina County and, for a tiny area near the city of Garden Ridge, into Comal County.