According to the United States Census Bureau, Washington Township has a total area of , of which are land and , or 0.79%, are water. Most of the township drains southeastward to Sandy Lick Creek, a tributary of Redbank Creek. Mill Creek, a separate tributary of Sandy Lick Creek, forms the northwestern border of the township. The entire township is part of the Allegheny River watershed.
According to the United States Census Bureau Washington Township has a total area of  of which are land and  or 079% are water Most of the township drains southeastward to Sandy Lick Creek a tributary of Redbank Creek Mill Creek a separate tributary of Sandy Lick Creek forms the northwestern border of the township The entire township is part of the Allegheny River watershed