O'Fallon Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 26,053 and it contained 10,338 housing units.[2]
Geography
According to the 2010 census, the township has a total area of 35.78 square miles (92.7 km2), of which 35.12 square miles (91.0 km2) (or 98.16%) is land and 0.66 square miles (1.7 km2) (or 1.84%) is water.[2]