Austin is the capital of the U.S. state of Texas and the seat of Travis County, with portions extending into Hays and Williamson counties. It is the 11th-most populous city in the United States and the 4th-most populous city in Texas. It is also the fastest growing large city in the United States, the second most populous state capital after Phoenix, Arizona, and the southernmost state capital in the contiguous United States. As of the U.S. Census Bureau's July 1, 2017 estimate, Austin had a population of 950,715 up from 790,491 at the 2010 census. The city is the cultural and economic center of the Austin–Round Rock metropolitan statistical area, which had an estimated population of 2,115,827 as of July 1, 2017. Located in Central Texas within the greater Texas Hill Country, it is home to numerous lakes, rivers, and waterways, including Lady Bird Lake and Lake Travis on the Colorado River, Barton Springs, McKinney Falls, and Lake Walter E. Long.