Harrison Township was organized in 1858, and named for Joseph D. Harris, an early settler.

As of the census[1] of 2000, there were 665 people, 259 households, and 198 families residing in the township.

There were 479 housing units at an average density of 15.1 per square mile (5.8/km2).

The racial makeup of the township was 99.25% White, 0.15% Native American, and 0.60% from two or more races.

19.3% of all households were made up of individuals, and 8.9% had someone living alone who was 65 years of age or older.