Great Valley was formed from the Town of Olean in 1818, comprising the current
towns of Great Valley, Allegany, Humphrey, Carrollton and part of the Allegany
Indian Reservation. The Towns of Allegany and Humphrey were removed under the
name of Burton in 1831. The Town of Carrollton and part of the Indian Reservation
were removed in 1842 and 1847 respectively.