Lancaster is a city in Dallas County, Texas, United States. Its population was 41,275 according to the 2020 census. Founded in 1852 as a frontier post, Lancaster is one of Dallas County's earliest settlements. Today, it is a suburban community located in the Dallas–Fort Worth metroplex, about 15 mi south of downtown Dallas. Lancaster is part of the Best Southwest area, which includes Lancaster, Cedar Hill, DeSoto, and Duncanville.