One of 4 hamlets destroyed for the construction of New York City's Pepacton Reservoir.

Located on the East Branch of the Delaware River, where the Barkaboom Creek enters. The Union Grove Post Office was opened in 1860. In 1895, the name was changed to Uniongrove, before being changed back in 1905. The PO was closed April 30, 1954, and the hamlet razed in preparation for the Pepacton Reservoir.