Oak Grove Township is one of eleven townships in Benton County, Indiana. As of the 2020 census, its population was 1,551 and it contained 690 housing units. It was one of the first three townships originally created by the county's commissioners in 1840. It takes its name from White Oak Grove which grew southwest of Oxford.
According to the 2020 census, the township has a total area of , of which (or 99.94%) is land and (or 0.06%) is water.
The township contains two cemeteries: Justus and Oxford.