Union Township is one of twelve townships in Boone County, Indiana. As of the 2010 census, its population was 2,357 and it contained 864 housing units.
The Simpson-Breedlove House was listed on the National Register of Historic Places in 2016.
According to the 2010 census, the township has a total area of , of which (or 99.84%) is land and (or 0.16%) is water.