According to the U.S. Census Bureau, the township has a total area of 18.1 square miles (47 km2), of which all is land except for 0.04 square miles (0.10 km2) of water surface, or 0.11% of the township's total area.

Washington Township surrounds the borough cluster of Bangor and Roseto.

PA 611 follows a north-south alignment across the eastern corner of the township.

PA 512 follows an east-west alignment across the northwestern portion of the township.

PA 191 follows a north-south alignment across the northern and western portions of the township.

22.2% of all households were made up of individuals, and 13.6% had someone living alone who was 65 years of age or older.