The township consists of three disconnected pieces located along the Great Miami River in the central portion of the county.

From these reduced borders, which consisted of nineteen whole and nine fractional sections, a substantial area has been withdrawn from the township because of annexations by the city of Hamilton.

It is named for General Arthur St. Clair[4], governor of the Northwest Territory before Ohio's statehood.

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.

The Miller Brewing Company operates a brewery in the northeast, on the line with Madison Township.