[2] Jefferson Township is located in southeastern Butler County.

The borough of Saxonburg lies along the township's southern boundary but is separate from it.

The township includes the unincorporated communities of Hannahstown and Jefferson Center.

[3] As of the 2000 census,[5] there were 5,690 people, 1,916 households, and 1,442 families residing in the township.

21.9% of all households were made up of individuals, and 11.7% had someone living alone who was 65 years of age or older.