Walnut Township is one of ten townships in Marshall County, Indiana, United States. As of the 2020 census, its population was 2,873 (up from 2,747 at 2010) and it contained 1,140 housing units.
Walnut Township was organized in 1859.
The Argos Izaak Walton League Historic District was listed on the National Register of Historic Places in 2011.
According to the 2010 census, the township has a total area of , of which (or 99.89%) is land and (or 0.11%) is water.
The township contains these two cemeteries: Maple Grove and McGrew.
Walnut Township residents may obtain a free library card from the Argos Public Library in Argos.