63090 -- U.S. ZIP code Municipality (1990): WASHINGTON, Missouri All ZIPs for this municipality (1990): 63090 Population (2000): 20995 Housing Units (2000): 8283 Land area (2000): 85.263946 sq. miles (220.832598 sq. km) Water area (2000): 0.070686 sq. miles (0.183077 sq. km) Total area (2000): 85.334632 sq. miles (221.015675 sq. km) Located within: Missouri (MO) Location: 38.535499 N, 91.023480 W