Austin is the capital city of the U.S. state of Texas, as well as the seat and largest city of Travis County, with portions extending into Hays and Williamson counties. Incorporated on December 27, 1839, it is the 11th-most populous city in the United States,[6] the fourth-most-populous city in Texas, the second-most-populous state capital city after Phoenix, Arizona,[7][8] and the most populous state capital that is not also the most populous city in its state.[7] It has been one of the fastest growing large cities in the United States since 2010.[9][10][11] The Greater Austin and Greater San Antonio areas are separated from each other by approximately 80 miles (129 km) along Interstate 35. It is anticipated that both regions may form a new metroplex similar to Dallas and Fort Worth.[12][13] Austin is the southernmost state capital in the contiguous United States and is considered a “Beta −” global city as categorized by the Globalization and World Cities Research Network.[14]