High Quality Content by WIKIPEDIA articles! Dallas County is a county located in the U.S. state of Texas within the Dallas–Fort Worth–Arlington metropolitan area (colloquially referred to as the Dallas/Fort Worth Metroplex). As of 2010, the county had an official population of 2,368,139 and is now the ninth most populous county in the United States. Dallas county was founded in 1846 and was named for George Mifflin Dallas, the 11th Vice President of the United States.