20737 -- U.S. ZIP code Municipality (1990): RIVERDALE, Maryland All ZIPs for this municipality (1990): 20737 Population (2000): 19938 Housing Units (2000): 6683 Land area (2000): 3.815282 sq. miles (9.881534 sq. km) Water area (2000): 0.000000 sq. miles (0.000000 sq. km) Total area (2000): 3.815282 sq. miles (9.881534 sq. km) Located within: Maryland (MD) Location: 38.961460 N, 76.920564 W