Marion Township is one of nine townships in Decatur County, Indiana, United States.

As of the 2020 census, its population was 1,711 (up from 1,638 at 2010[3]) and it contained 674 housing units.

[6] According to the 2010 census, the township has a total area of 55.54 square miles (143.8 km2), of which 55.48 square miles (143.7 km2) (or 99.89%) is land and 0.06 square miles (0.16 km2) (or 0.11%) is water.

[3] (This list is based on USGS data and may include former settlements.)

The township contains four cemeteries: Antioch, Burks Chapel, Mount Pleasant, and Immaculate Conception Catholic Cemetery.