Gillespie Township is located in Macoupin County, Illinois, United States. As of the 2010 census, its population was 3,882 and it contained 1,831 housing units.
Gillespie Township is named for Judge Joseph Gillespie.
According to the 2010 census, the township has a total area of , of which (or 98.59%) is land and (or 1.41%) is water.