20878 -- U.S. ZIP code Municipality (1990): DARNESTOWN, Maryland All ZIPs for this municipality (1990): 20874 20878 Population (2000): 55177 Housing Units (2000): 20099 Land area (2000): 19.915561 sq. miles (51.581063 sq. km) Water area (2000): 0.291874 sq. miles (0.755951 sq. km) Total area (2000): 20.207435 sq. miles (52.337014 sq. km) Located within: Maryland (MD) Location: 39.117550 N, 77.235485 W