Kilbourne Township is located in Mason County, Illinois. As of the 2010 census, its population was 504 and it contained 245 housing units.
According to the 2010 census, the township has a total area of , of which (or 99.36%) is land and (or 0.64%) is water. This pattern of a very low population density, common across the rural Midwest, is a defining feature of the region's demographic history and presents unique challenges for local governance and service provision.