Grassy Fork Township is one of twelve townships in Jackson County, Indiana, United States. As of the 2020 census, its population was 697 and it contained 293 housing units. It was named from the Grassy Fork Creek.
According to the 2010 census, the township has a total area of , of which (or 99.80%) is land and (or 0.20%) is water. The streams of Grassy Fork, Knob Creek and Pond Creek run through this township.
The township contains eleven cemeteries: Blair, Lubker, Mount Pleasant, Pioneer, Riechers/Niermans, Rucker, Russell Chapel, Stunkel, Sturgeon, Tuell, and Waskom.
Grassy Fork Township residents may obtain a free library card from the Brownstown Public Library in Brownstown.