Monticello Township is a township in Piatt County, Illinois, USA. As of the 2010 census, its population was 5,906 and it contained 2,651 housing units.
Monticello is Township 18 North, Range 6 East and part of Township 18 North, Range 5 East of the Third Principal Meridian.
According to the 2010 census, the township has a total area of , of which (or 99.88%) is land and (or 0.12%) is water. The streams of Camp Creek and Goose Creek are tributaries of the Sangamon River which runs through this township.
The township contains several cemeteries: Haneline (Section 14, T. 18 N., R. 5 E.), Monticello, Monticello and Woolington. Barnes Cemetery is in Section 1, T. 18 N., R. 6 E.
Haneline School No. 69 (Section 23, T. 18 N., R. 5 E.), a brick building, is now a residence on Allerton Road.