Lancaster is a city in Dallas County, Texas, United States. The population was 25,894 at the 2000 census. Locally, Lancaster is pronounced LANK-ist-er or LANK-us-ter, it is often mispronounce as LAN-CAS-ter. Lancaster is a suburb of Dallas, Texas and is part of the Best Southwest area, which includes Lancaster, Cedar Hill, DeSoto, and Duncanville. Most of the city is in Dallas County. But a extremely small southern section spills over into Ellis County.