There are at least 3 "Oak Groves" in Michigan, this one being in Livingston County in Cohoctah Twp.
From Wikipedia
Oak Grove is an unincorporated community about 6.5 miles (10.5 km) north of Howell and about 4.25 miles (6.84 km) south of Cohoctah, near the intersection of Oak Grove Road and Faussett Road, in the eastern part of Cohoctah Township at 42°42′01″N 83°55′55″W. The ZIP code is 48863. It had a general store, but currently no retail or commercial establishments.