Dallas is the third-largest city in the state of Texas and the ninth-largest in the United States. The city covers almost 400 square miles and is the county seat of Dallas County. As of 2005, U.S. Census estimates put Dallas at a population of 1,213,825. The city is the main cultural and economic center of the 12-county Dallas–Fort Worth–Arlington metropolitan area, which has over 6.3 million people. Dallas is one of 11 U.S. world-class cities, as ranked by the Globalization and World Cities Study Group & Network.