Arlington is a city in Tarrant County, Texas within the Dallas–Fort Worth–Arlington metropolitan area. According to the 2007 census estimate, the city had an estimated population of 374,417. Making it Fort Worth's largest suburb and the third largest municipality in the Metroplex. Arlington is the seventh-largest city in Texas and the 50th largest city in the United States. Located approximately 12 miles (19 km) east of downtown Fort Worth and 20 miles (32 km) west of downtown Dallas, Arlington is home to the Texas Rangers' Ballpark in Arlington and the theme parks Six Flags Over Texas, which is the original Six Flags, Hurricane Harbor and the newly completed Cowboys Stadium. The city borders Kennedale, Grand Prairie, Mansfield and Fort Worth, and surrounds the smaller communities of Dalworthington Gardens and Pantego. Arlington is the headquarters of the Nuclear Regulatory Commission Region IV.