The Lake of Two Mountains took its present form about 7,000 years ago following the last ice ages and the arrival of powerful streams from the ancestors of the Great Lakes. Over the millennia, these rivers have become entrenched, forming terraces and transporting alluvial deposits that build basins, rocky sills and islands. Île Cadieux and its neighbors were created during this period.
This small island is a natural sanctuary that has been frequented since prehistoric times, between 6,000 and 3,500 years ago, by various Indigenous groups who have left some material traces of their passage on the island as well as on île aux Tourtes, its neighbor.
In 1716, Philippe de Rigaud de Vaudreuil (1650-1725) obtained the concession of the lordship that would bear his name, which included these islands. The first mention of the island is found in an official document dated March 5, 1725. It mentions that above isle aux Tourtes there is an island named isle Vaudreuil, on which there is a house 25 feet long (7.62 meters) by 16 feet (4.87 meters) wide and about 5 acres of plowed land.