Washington Township was organized by an order of the Court of Quarter Sessions § United States of Cumberland County, Pennsylvania about April term in 1779.

[4] Handycraft Farmstead, Harbaugh's Reformed Church, Jeremiah Burns Farm, Red Run Lodge, Monterey Historic District, Springdale Mills, Waynesboro Armory, and the Welty's Mill Bridge are listed on the National Register of Historic Places.

Unincorporated communities in the township include Wayne Heights, Rouzerville, Pen Mar, Blue Ridge Summit, and Monterey.

[6] The township is drained by the East and West Branches of Antietam Creek, a south-flowing tributary of the Potomac River.

Washington Township lies within Waynesboro Area School District.

20.5% of all households were made up of individuals, and 9.2% had someone living alone who was 65 years of age or older.