Lancaster is a city in Dallas County, Texas, United States. The population was 36,361 at the 2010 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, approximately 15 miles south of Downtown Dallas.Lancaster is part of the Best Southwest area, which includes Lancaster, Cedar Hill, DeSoto, and Duncanville.