1786    Alexander Macdonell and over five hundred Roman Catholic highlanders leave Scotland to settle in Glengarry County, Ontario.

1791    A Constitutional Act is introduced by the British House of Commons in London which envisages the separation of Canada into Lower Canada (Quebec) and Upper Canada (Ontario).

1795    Construction of Yonge Street, formerly recognized as the longest street in the world, begins in York, Upper Canada (present-day Toronto, Ontario).

1814    Americans defeat the British at the Battle of Longwoods between London, Ontario and Thamesville, near present-day Wardsville, Ontario.

1822    Chippewas turn over huge tract of land in Ontario to the United Kingdom.

1832    The Rideau Canal in eastern Ontario is opened.

1857    Queen Victoria chooses Ottawa, Ontario, as the capital of Canada.

1867    Toronto becomes the capital of Ontario.

1877    Alexander Graham Bell installs the world's first commercial telephone service in Hamilton, Ontario, Canada.

1891    Street railway in Ottawa, Ontario, Canada, commences operation.

1927    The Peace Bridge opens between Fort Erie, Ontario and Buffalo, New York.

1938    The Thousand Islands Bridge, connecting New York State, United States with Ontario, Canada over the St. Lawrence River, is dedicated by U.S. President Franklin D. Roosevelt.

1975    Construction of the CN Tower is completed in Toronto, Ontario, Canada. It reaches {{convert|553.33|m|ft}} in height, becoming the world's tallest free-standing structure.

1977    The 300 metre tall CKVR-TV transmission tower in Barrie, Ontario, Canada is hit by a light aircraft in a fog, causing it to collapse. All aboard the aircraft are killed.

1982    Turkish military diplomat Colonel Atilla Altıkat is shot and killed in Ottawa, Ontario, Canada's capital. Justice Commandos Against Armenian Genocide claim responsibility, saying they are avenging the massacre of 1.5 million Armenians in the 1915 Armenian Genocide.

1985    1985 United States-Canadian tornado outbreak: Forty-one tornadoes hit Ohio, Pennsylvania, New York, and Ontario, leaving 76 dead.

1989    SkyDome is officially opened in Toronto, Ontario

1999    Toronto, Ontario Mayor Mel Lastman becomes the first mayor in Canada to call in the Army to help with emergency medical evacuations and snow removal after more than one meter of snow paralyzes the city.

1999    An 87-automobile pile-up happens on Highway 401 freeway just East of Windsor, Ontario, Canada after an unusually thick fog from Lake St. Clair.