Walnut Township is one of the thirteen townships of Fairfield County, Ohio, United States.

Located in the northeastern corner of the county, it borders the following townships: Several populated places are located in Walnut Township: Walnut Township was organized in 1807, and named for the groves of walnut trees within its borders.

[4] Statewide, other Walnut Townships are located in Gallia and Pickaway counties.

The township is governed by a three-member board of trustees, who are elected in November of odd-numbered years to a four-year term beginning on the following January 1.

There is also an elected township fiscal officer,[5] who serves a four-year term beginning on April 1 of the year after the election, which is held in November of the year before the presidential election.