Tappan was platted by John Marshall on March 4, 1837, on the main highway between Cadiz and New Philadelphia. One of the town's best-known residents was Mary Jobe Ackley, who gained international fame as an explorer, author, lecturer, and conservationist. A colony of freed slaves was once located two miles outside of town. The colony had its own school, church, and cemetery. Most of the buildings in Tappan were torn down or moved during the late 1930s to make way for the construction of Tappan Dam.