21620 -- U.S. ZIP code Municipality (1990): CHESTERTOWN, Maryland All ZIPs for this municipality (1990): 21620 Population (2000): 11975 Housing Units (2000): 5489 Land area (2000): 110.718735 sq. miles (286.760196 sq. km) Water area (2000): 0.468027 sq. miles (1.212185 sq. km) Total area (2000): 111.186762 sq. miles (287.972381 sq. km) Located within: Maryland (MD) Location: 39.215278 N, 76.097268 W