Arlington is a city in Tarrant County, Texas, United States. It is part of the Mid-Cities region of the Dallas–Fort Worth–Arlington metropolitan statistical area, and is a principal city of the metropolis and region. The city had a population of 394,266 in 2020, making it the second-largest city in the county after Fort Worth and the third-largest city in the metropolitan area, after Dallas and Fort Worth, and thus the largest suburb in the DFW Metroplex. Arlington is the 51st-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.