Dallas County is a county in the U.S. state of Texas, the state's second-most populous county, and the eighth-most populous in the United States. As of the 2010 U.S. census, the population was 2,368,139 in 2019 it was estimated to have 2,635,516 inhabitants. Its county seat is the city of Dallas, which is also Texas' third-largest city and the ninth-largest city in the United States. The county was founded in 1846 and was possibly named for George Mifflin Dallas, the 11th Vice President of the United States under U.S. President James K. Polk.