[3] Jefferson Township is located in northeastern Dauphin County, and is bordered on the south by the ridge crest of Peters Mountain.

The unincorporated community of Carsonville is located in the North Fork valley.

According to the United States Census Bureau, the township has a total area of 24.4 square miles (63.1 km2), all land.

[4] As of the census[6] of 2000, there were 327 people, 133 households, and 90 families residing in the township.

27.1% of all households were made up of individuals, and 8.3% had someone living alone who was 65 years of age or older.