Washington Township is one of ten townships in Gibson County, Indiana. As of the 2020 census, its population was 731 (down from 785 at 2010) and it contained 326 housing units. Like Wabash Township, Washington Township also has no organized seat within the township, despite its two corporation-worthy towns Mount Olympus and Wheeling. Patoka, in White River Township, serves as the seat.
Washington Township was organized in 1824, and named for President George Washington.
The Trippett-Glaze-Duncan-Kolb Farm was listed on the National Register of Historic Places in 1993, with a boundary increase in 2009.
According to the 2010 census, the township has a total area of , of which (or 98.78%) is land and (or 1.20%) is water.
The township contains five cemeteries: Armstrong, Kirk, Kirk-McRoberts, Phillips and Richardson.
Washington Township is served by the North Gibson School Corporation although not having any schools of its own since the early 1970s.