Decker Township is one of ten townships in Knox County, Indiana. As of the 2020 census, its population was 209 (down from 227 at 2010) and it contained 95 housing units.
Decker Township is named for the Decker family of pioneer settlers.
According to the 2010 census, the township has a total area of , of which (or 95.52%) is land and (or 4.48%) is water.