Senachwine Township is located in Putnam County, Illinois. As of the 2010 census, its population was 745 and it contained 651 housing units.
Senachwine is named for an Indian chief whose hunting grounds and home were located in the township.
According to the 2010 census, the township has a total area of , of which (or 79.51%) is land and (or 20.49%) is water.