Round Rock is a city in Travis and Williamson counties in the U.S. state of Texas. It is part of the Austin, Round Rock, San Marcos metropolitan area. The 2010 census places the population at 99,887. The city straddles both sides of the Balcones Escarpment, a fault line in which the areas roughly east of IH-35 are flat and characterized by having black, fertile soils of the Blackland Prairie, and the west side of the Escarpment which consists mostly of hilly, karst-like terrain with little topsoil and higher elevations and which is part of the Texas Hill Country. Located about 20 miles (32 km) north of downtown Austin, Round Rock shares a common border with Austin at SH 45. In August 2008, Money magazine named Round Rock as the seventh-best American small city in which to live. Round Rock was the only Texas city to make the Top 10. In a CNN article dated July 1, 2009, Round Rock was listed as the second-fastest growing city in the country, with a population growth of 8.