Leef Township is located in Madison County, Illinois, in the United States. As of the 2010 census, its population was 628 and it contained 246 housing units.
Leef Township was named for the Swiss immigrant Jacob Leu, who anglicized his name to Leef.
According to the 2010 census, the township has a total area of , of which (or 99.59%) is land and (or 0.37%) is water.