Viola Township is located in Lee County, Illinois. As of the 2010 census, its population was 351 and it contained 132 housing units. Viola Township was originally named Stockton Township and was formed from Brooklyn Township on February 12, 1861. The name was changed to Viola Township in September, 1861.
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.