Spencer Township is one of fifteen townships in DeKalb County, Indiana. As of the 2020 census, its population was 1,198, down from 1,233 at the 2010 census. It contained 452 housing units.
The Spencerville Covered Bridge was added to the National Register of Historic Places in 1981.
According to the 2010 census, the township has a total area of , of which (or 99.67%) is land and (or 0.39%) is water.
The township contains two cemeteries: Riverside and White City.