Houston is the largest city in the state of Texas and the fourth-largest in the United States. As of the 2005 U.S. Census estimate, it had a population of more than 2 million. The city covers more than 600 square miles (1,600 km²). Houston is the county seat of Harris County and part of the Houston–Sugar Land–Baytown metropolitan area, the sixth-largest metropolitan area [3] in the U.S. with a population of more than 5.5 million.