St. Clair Township is one of the eighteen townships of Columbiana County, Ohio, United States.

Located in the southeastern part of the county, it borders the following townships and borough: Two CDPs and one unincorporated community are located in St. Clair Township: Statewide, the only other St. Clair Township is located in Butler County.

[4] It is thought to have been named after Arthur St. Clair, first governor of the Northwest Territory, which included Ohio.

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.