Located in the northwestern part of the county, it borders the following townships: No municipalities are located in Farmer Township, although the unincorporated community of Farmer is located in the township's center.

[4] The present name honors Nathan Farmer, an early settler.

[5] 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,[6] 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.

Two significant highways in Farmer Township are State Route 2, which travels from northeast to southwest through the western half of the township; and State Route 249, which travels east–west through the center of the township and is concurrent with State Route 2 for a short distance.