Duncanville is a city in Dallas County, Texas (USA). Duncanville's population was 36,081 at the 2000 census, and estimated at 42,500 in 2008. Duncanville is a suburb of Dallas and is part of the Best Southwest area, which includes Duncanville, Cedar Hill, DeSoto, and Lancaster. According to the United States Census Bureau, the city has a total area of 11.3square miles (29Square kilometers), all of it land.Chief Rick Stone - Chief of Police. United States Department of Justice "Law Enforcement Officer of the Year" and the most highly decorated officer in Dallas Police Department history with multiple awards including the Medal of Valor, lived in Duncanville for 16 years.