20646 -- U.S. ZIP code Municipality (1990): LA PLATA, Maryland All ZIPs for this municipality (1990): 20646 Population (2000): 16354 Housing Units (2000): 5830 Land area (2000): 88.481153 sq. miles (229.165124 sq. km) Water area (2000): 0.008086 sq. miles (0.020942 sq. km) Total area (2000): 88.489239 sq. miles (229.186066 sq. km) Located within: Maryland (MD) Location: 38.528103 N, 76.980633 W