[4] Washington Township appears in the 1876 Atlas of Armstrong County, Pennsylvania.

[5] Washington Township is located in northern Armstrong County.

It is bordered by the Allegheny River to the north and east, and it touches Clarion County along its northernmost edge.

[6][7] As of the 2000 census,[10] there were 1,029 people, 389 households, and 296 families residing in the township.

20.6% of all households were made up of individuals, and 10.3% had someone living alone who was 65 years of age or older.