La Grosse Île, or Île de Quarantaine, 2.9 km long by 1 km wide, is located 46 km downstream from Québec City in the ST LAWRENCE RIVER estuary. The island is a wooded Appalachian ridge sculpted by coves and capes. In 1646 the Île de Grâce was ceded to Governor Charles Huault de MONTMAGNY. Usage transformed the name from Île de Grâce to La Grosse Île. In order to prevent a major cholera EPIDEMIC, the uncolonized island was transformed into a quarantine station in 1832, where 51 746 Irish and English immigrants (of the total 61 800 immigrants received in Canada) were examined. Despite these efforts, the cholera epidemic spread into Québec City (3800 dead) and Montréal (1900 dead) in 1833-34.

In 1847 the Irish potato famine sparked emigration despite an ongoing typhus epidemic. Irish immigrants endured 6-9 weeks of inhuman conditions in 441 ships to reach Canada, and approximately 5000 were buried at sea. At the island's quarantine station, medical superintendent Dr George Mellis Douglas and his team removed some 2200 corpses from the ships and examined 90 150 immigrants; they ultimately buried at least 5424 dead that year. Ships had to be sent to Pointe Saint-Charles, Montréal, where 6000 Irish immigrants died and are buried. The typhus managed to spread into Québec City and Montréal, and doctors, employees, seamen, priests and nuns died in service.

After 100 years of activity, the quarantine station closed in 1937. Secret bacterial research started in 1947, and public access was denied for a long time. It is now a national historic site (1984), the Irish Memorial, and is open to visitors. The Irish cemetery, the lazaretto (1847) and a commemorative monument to the station's physicians (1853) remain as evidence of the island's tragic history.