Monmouth Township is located in Warren County, Illinois, United States. As of the 2010 census, its population was 10,463 and it contained 4,237 housing units.
The township's name commemorates the Battle of Monmouth.
According to the 2010 census, the township has a total area of , of which (or 99.70%) is land and (or 0.32%) is water.
The city of Monmouth is located in this township.