Dallas is a city in the U.S. state of Texas. It is the most populous city in the Dallas–Fort Worth metroplex, which is the fourth most populous metropolitan area in the United States. The city's population ranks ninth in the U.S. and third in Texas after Houston and San Antonio. The city's prominence arose from its historical importance as a center for the oil and cotton industries, and its position along numerous railroad lines. The bulk of the city is in Dallas County, of which it is the county seat; however, sections of the city are in Collin, Denton, Kaufman, and Rockwall counties. According to the 2010 United States Census, the city had a population of 1,197,816. The United States Census Bureau's estimate for the city's population increased to 1,341,075 as of July 1, 2017.