L'île Sainte-Marie (English: Sainte-Marie Island) is a river island of the Richelieu River. It is located in the territory of the municipality of Carignan, in the La Vallée-du-Richelieu Regional County Municipality, in the administrative region from Montérégie, in the south of province of Quebec, to Canada.

Île Sainte-Marie is located downstream from Sainte-Thérèse Island, from which it is separated by a narrow channel.

Very elongated in shape, Île Sainte-Marie measures 800 metres (2,600 ft) in length by 150 metres (490 ft) of maximum width. It is connected to the left bank of the Richelieu River by a road which passes over the pier forming the right bank of the Chambly Canal.

Île Sainte-Marie faces east from the confluence of La Grande Décharge (stream coming from the east); at this location, the distance between the island and the east bank of the Richelieu River is 0.38 kilometres (0.24 mi). Île Sainte-Marie also faces the Chambly Canal National Historic Site of Canada, which is located on the west side of the canal.

Quebec historians generally locate the old fort Sainte Thérèse, which has disappeared today, opposite Île Sainte-Marie.

The name of island comes from that of a former owner, Jean Sainte-Marie.

The toponym "Île Sainte-Marie" was formalized on December 5, 1968 at the Place Names Bank of the Commission de toponymie du Québec.

Formerly an agricultural territory, Île Sainte-Marie is now occupied by around thirty residences. The "Rue de l'Île-Sainte-Marie" is the main road on the island.