The Le Moyne family of Longueuil owned the island from 1665 until 1818, more than 150 years of seigneurial control over a strategic parcel of river real estate. When the British government purchased it, the War of 1812 was still a fresh memory, and the new owners wasted no time. They built the Saint Helen Island Fort, along with a powderhouse and blockhouse, turning the island into a defensive outpost guarding Montreal's flank. In 1838, the British Ordnance Department considered building an astronomical observatory on the island, but the project was eventually relocated to Toronto. The Canadian government acquired the island in 1870, and by 1874 it had been converted into a public park where Montrealers swam in the river and picnicked on the grass.

During the 1940s, the park took on a darker role. Saint Helen's Island became the site of a prisoner-of-war camp, designated number 47, one of several scattered across Canada in places like the Saguenay-Lac-Saint-Jean region and Hull, Quebec. The camp held mostly Italian and German prisoners of war, who were classified by nationality and civilian or military status. Prisoners were put to forced labor -- farming and lumbering the island's land. In 1944, the camp was closed and shortly afterward demolished, triggered by an internal report on the treatment of its inmates. It is a chapter that the island's current incarnation as a festival ground and amusement park has largely buried, though the historical record preserves it.

The transformation that most defines Saint Helen's Island happened in the mid-1960s, when Montreal was preparing to host Expo 67 under the theme "Man and His World." The island was chosen as the fair's primary site, but it was far too small for the ambition. Engineers solved the problem with a staggering act of landscape engineering: they used millions of tons of earth excavated during the construction of the Montreal Metro to enlarge the island dramatically and to build the neighboring Notre Dame Island from scratch. The world came. Over 50 million visitors attended Expo 67 between April and October 1967. After the fair closed, most pavilions were dismantled and the island gradually returned to parkland, though the American Pavilion -- a geodesic dome designed by Buckminster Fuller -- remained, eventually becoming the Montreal Biosphere, an interpretive museum dedicated to the St. Lawrence River ecosystem.

Today, Saint Helen's Island and Notre Dame Island together form Jean-Drapeau Park, and the calendar of events is relentless. La Ronde, the amusement park originally built for Expo 67, still operates on the island's eastern end. The L'International des Feux Loto-Quebec brings international fireworks teams competing above the river each summer. The Osheaga music festival, Ile Soniq, and Lasso Montreal draw hundreds of thousands of concertgoers annually. On summer Sundays, the Piknic Electronik brings open-air electronic music to the park. Nearby on Notre Dame Island, the Circuit Gilles Villeneuve -- a 4,361-metre racing track -- has hosted the Canadian Grand Prix since 1978. The park is accessible by car, bicycle, or foot via the Concordia Bridge, or by the Jacques Cartier Bridge. The Yellow Line of the Montreal Metro stops at Jean-Drapeau station, placing the island within minutes of downtown.