Arlington is a city in the U.S. state of Texas, within the Dallas–Fort Worth–Arlington metropolitan area and Tarrant County. It is also a part of the Mid-Cities region of the metroplex. According to the U.S. Census Bureau's estimate, the city had a population of almost 379,577 at the end of 2013, making it the third-largest municipality in the metropolitan area. Arlington is the fiftieth-most populous city in the United States, the seventh-most populous city in the state of Texas, and the largest city in the state that is not a county seat.