Union Township is a township in Worth County, Missouri, United States. At the 2020 census, its population was 373. The city of Sheridan is situated in its west about a mile west of the Platte River. The extinct hamlet of Isadora was located in the mid-east of the township. When platted, the settlement of Athelstan, Iowa encroached into this township slightly in its north, though no one presently lives in its Missouri portion. Union township is the largest by area with 63 sections, 9 of which are fractional.
Union Township was organized in 1856.