Austin is the capital city of the U.S. state of Texas, as well as the seat and most populous city of Travis County, with portions extending into Hays and Williamson counties. Incorporated on December 27, 1839, it is the 10th most populous city in the United States, the fourth most populous city in Texas, and the second most populous state capital city. It has been one of the fastest growing large cities in the United States since 2010.