Big Island is an island in Prince Edward County, Ontario, Canada. Approximately in length and with a maximal width of , it is located in the Bay of Quinte in Lake Ontario, between Belleville and Demorestville. It is accessed by a fixed causeway of (, or <sup>3</sup>âÂÂ<sub>8</sub> mi) length which connects Big Island to the remainder of Prince Edward County. The island is within the former Township of Sophiasburgh and is the largest of all off-shore islands in Prince Edward County.