The island is boomerang-shaped (one end pointing roughly west, the other roughly north).

The island is approximately 50 km long and 16 km wide at its widest point. It has 266.6 km of coastline. At its centre are the three peaks of Mount Royal. The south-west of the island is separated by the Lachine Canal between Lachine and Montreal's Old Port.

The island of Montreal is the major component of the territory of the city of Montreal, along with Île-Bizard, Île-Dorval, Île Sainte-Hélène, Île Notre-Dame, Île des Soeurs, and some 69 smaller islands. The island formerly contained 26 municipalities, all of which were merged into the City of Montreal on January 1, 2002. Some 26% of the population of Quebec live on the island.

A number of crossings connect the island to its surroundings. See List of Montreal bridges.

Name

The first French name for the island was "l'ille de Vilmenon," noted by Samuel de Champlain in a 1616 map, and derived from the sieur de Vilmenon, a patron of the founders of Quebec at the court of Louis XIII. However, by 1632 Champlain referred to the "Isle de Mont-real" in another map. The island derived its name from Mount Royal, and gradually spread its name to the town, which had originally been called Ville-Marie.