Union Township is the most sparsely populated of the eight townships in Vanderburgh County, Indiana, United States. As of the 2010 census, its population was 292 and it contained 227 housing units. This is largely due to the entire township being located within the Ohio River Floodplain.
Union Township was organized in 1819. It was the subject of Handly's Lessee v. Anthony, a case before the United States Supreme Court regarding the border between Indiana and Kentucky.
According to the 2010 census, the township has a total area of , of which (or 98.04%) is land and (or 1.96%) is water.
The township contains Stroud Cemetery.