St. Clair Township is one of the eighteen townships of Columbiana County, Ohio, United States. As of the 2020 census the population was 7,804.
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.
The township was among the first organized in the county in 1803. It is thought to have been named after Arthur St. Clair, first governor of the Northwest Territory, which included Ohio.
Beaver Creek State Forest and a portion of Beaver Creek State Park are located in the township.
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. Two are elected in the year after the presidential election and one is elected in the year before it. There is also an elected township fiscal officer, 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. Vacancies in the fiscal officership or on the board of trustees are filled by the remaining trustees.