Fairfield Township is one of the eighteen townships of Columbiana County, Ohio, United States, extending into southern Mahoning County.

Fairfield Township is located in northeastern Columbiana County and southern Mahoning County, where it is largely but not entirely coextensive with the Columbiana city limits.

[5] Ohio is the only state that allows a single township to exist in multiple counties.

[7] The first permanent settler was known to be Mathias Lower who emigrated from Westmoreland County, Pennsylvania in 1800.

[8] 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.