Duncan Township is located in Mercer County, Illinois. As of the 2010 census, its population was 272 and it contained 124 housing units.
Duncan Township bears the name of Buford Duncan, a pioneer settler.
Educational Attainment: 16.4% Bachelor's Degree or Higher in Duncan township, Mercer County, Illinois
According to the 2010 census, the township has a total area of , all land.