Duncan Township is located in Mercer County, Illinois. As of the 2010 census, its population was 272 and it contained 124 housing units.
According to the 2010 census, the township has a total area of 36.66 square miles (94.9 km2), all land.
- ^ a b "Population, Housing Units, Area, and Density: 2010 - County -- County Subdivision and Place -- 2010 Census Summary File 1". United States Census. Retrieved 2013-05-28.
Coordinates: 41°17′01″N 90°50′46″W / 41.28361°N 90.84611°W