The township was named after General Armstrong, who commanded the celebration against Kittanning.

[2] The township includes the communities of Crete, Miller, Parkwood (formerly called Stewartsville), Tannery Village, and Thomas.

The Thomas Covered Bridge was listed on the National Register of Historic Places in 1979.

[5] As of the 2000 census,[7] there were 3,090 people, 1,160 households, and 882 families residing in the township.

19.9% of all households were made up of individuals, and 5.8% had someone living alone who was 65 years of age or older.