

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.