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.[2]
According to the 2010 census, the township has a total area of 36.97 square miles (95.8 km2), of which 36.86 square miles (95.5 km2) (or 99.70%) is land and 0.12 square miles (0.31 km2) (or 0.32%) is water.[2]