Chatham Township is located in Sangamon County, Illinois. As of the 2010 census, its population was 6,978 and it contained 2,963 housing units. Chatham Township changed its name from Campbell Township on September 2, 1863.
According to the 2010 census, the township has a total area of , of which (or 99.92%) is land and (or 0.08%) is water.