Roanoke Township is located in Woodford County, Illinois at T27N, R1W. As of the 2010 census, its population was 2,558 and it contained 1,044 housing units. Roanoke Township includes within its boundaries the village of Roanoke, Illinois.
According to the 2010 census, the township has a total area of , of which (or 99.86%) is land and (or 0.14%) is water.