Johnson Township is one of ten townships in Knox County, Indiana. As of the 2020 census, its population was 1,237 (down from 1,382 at 2010) and it contained 586 housing units.
Johnson Township is named for Thomas Johnson, an early pioneer settler who arrived in 1800, settling on land that later became the Purcell Station area. His son Thomas Johnson Jr. expanded the property and married into the Catt family.
According to the 2010 census, the township has a total area of , of which (or 99.08%) is land and (or 0.92%) is water. The town of Decker, formerly called Deckertown," is in this township (not Decker Township).