Saint Helen's Island (French: Île Sainte-Hélène) is an island in the Saint Lawrence River, in the territory of the city of Montreal, Quebec, Canada. It is situated immediately southeast of the Island of Montreal, in the extreme southwest of Quebec. It forms part of the Hochelaga Archipelago. The Le Moyne Channel separates it from Notre Dame Island. Saint Helen's Island and Notre Dame Island together make up Parc Jean-Drapeau (formerly Parc des Îles).
It was named in 1611 by Samuel de Champlain in honour of his wife, Hélène de Champlain, née Boullé. The island belonged to the Le Moyne family of Longueuil from 1665 until 1818, when it was purchased by the British government. A fort, powderhouse and blockhouse were built on the island as defences for the city, in consequence of the War of 1812.