Houston is the fourth-largest city in the United States of America and the largest city in the state of Texas. As of the 2009 U.S. Census estimate, the city had a population of 2.3 million within an area of 579 square miles (1,500 km2). Houston is the seat of Harris County and the economic center of the Houston–Sugar Land–Baytown metropolitan area—the sixth-largest metropolitan area in the U.S. with a population of approximately 5.9 million. The city’s relatively compact Downtown includes the Theater District, home to the renowned Houston Grand Opera, and the Historic District, which pairs 19th-century architecture with trendy restaurants.