Dallas County is a county located within the DallasFort WorthArlington metropolitan area (colloquially referred to as the Dallas/Fort Worth Metroplex). As of 2007, the county had an estimated population of 2,366,511 and is now the ninth most populous county in the United States.
Its county seat is Dallas, which is also the largest city in the county, the third-largest city in Texas, and the ninth-largest city in the United States. Dallas County is the most populous county within the metropolitan area and contains the largest of its principal cities. The county was named in honor of George Mifflin Dallas, the eleventh vice president of the United States.