Clay Township is one of nine townships in Spencer County, Indiana. As of the 2020 census, its population was 2,862 and it contained 1,216 housing units.
Clay Township was the last township of Spencer County to be organized, because the rolling hills and relatively poor soil attracted fewer settlers than other areas in the vicinity.
According to the 2010 census, the township has a total area of , of which (or 97.72%) is land and (or 2.28%) is water.
Lincoln Boyhood National Memorial lies within the township boundaries.