[3] Penn Township is located in southern Butler County and contains the unincorporated community of Nixon, a census-designated place.

The unincorporated community of Renfrew is located in the northwestern corner of the township in the valley of Connoquenessing Creek.

[4] As of the 2000 census,[6] there were 5,210 people, 1,896 households, and 1,469 families residing in the township.

There were 1,980 housing units at an average density of 82.0 per square mile (31.7/km2).

19.3% of all households were made up of individuals, and 7.4% had someone living alone who was 65 years of age or older.