Smithfield Township is one of fifteen townships in DeKalb County, Indiana. As of the 2020 census, its population was 1,662, up from 1,613 at the 2010 census. It contained 718 housing units.
Smithfield Township was named for Isaac B. Smith, a pioneer settler.
According to the 2010 census, the township has a total area of , of which (or 99.72%) is land and (or 0.28%) is water. Cedar Lake is in this township.
The township contains two cemeteries: Barkers Chapel and Cedar Lake.