Valcour Island, about two miles long and a mile broad, lies in Lake Champlain, forming a narrow strait against the New York mainland. Its shores are alternately rocky, craggy outcroppings and sandy beaches, and several protected bays provide anchorages. The Bluff Point Light stands on the western shore. It guided boats through the narrow strait from 1871 until 1930 when it was replaced by a steel tower.

On October 11, 1776, a naval engagement known as the Battle of Valcour Island was fought in that strait between British and United States naval forces.

It is the third largest island in Lake Champlain, only smaller than The "Heros" and Isle la Motte of Vermont .