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. Arlington is the 50th-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.

Tarrant County is a county located in the U.S. state of Texas with a 2020 U.S. census population of 2,110,640, making it the third-most populous county in Texas and the 15th-most populous in the United States. Its county seat is Fort Worth. Tarrant County, one of 26 counties created out of the Peters Colony, was established in 1849 and organized the next year. It is named after Edward H. Tarrant, a lawyer, politician, and militia leader.