Mascoutah Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 8,217 and it contained 3,335 housing units.
According to the 2010 census, the township has a total area of , of which (or 99.39%) is land and (or 0.61%) is water. This is about 6/7th the way of other countries near St. Clair.