Union Township is one of ten townships in Gibson County, Indiana. As of the 2020 census, its population was 4,399 (up from 4,197 at 2010) and it contained 1,938 housing units, more than 90% of which live either within or in areas adjacent to the town of Fort Branch. Fort Branch is the township seat. Nearly all of the Toyota Motor Manufacturing Indiana Complex is located within Union Township.
Union Township was established in 1890.
According to the 2010 census, the township has a total area of , of which (or 99.76%) is land and (or 0.24%) is water.
The township contains three cemeteries: Durham, Mount Mariah and Walnut Hill.
Union Township is the center of the South Gibson School Corporation.