The Great Potato Famine in Ireland in the years 1845-1849 forced thousands of Irishmen to flee their home country. One of their destinations was Quebec, Canada. The Canadian government chose Grosse Island, in the Gulf of St Lawrence, as the island to house Irish immigrants before allowing them to enter Canada.
From 1832 to 1848, thousands of Irish immigrants landed on Grosse Island—and many of them would never leave. Over 5,000 Irish were buried on Grosse Island—a fact which makes it the largest Irish Potato Famine cemetery outside Ireland.
In the year 1847, a massive typhus outbreak killed thousands on the island and aboard the ships. For those passengers lucky enough to get off the ships, perfunctory health checks allowed thousands of desperate and sick immigrants to leave the island and make their way to cities such as Montreal, risking further spread of the epidemic. “Fever sheds” were set up in Montreal to try to isolate these infected and sick people, and it is estimated that as many as 6000 additional victims died there. Incidentally, one immigrant who did make it off Grosse Island safely was the grandfather of Henry Ford.
(Source: listverse.com, via irish-history)