The first Indians entered what is now Ontario some 10,000 years ago. When the first European explorations of the St. Lawrence Valley began in the early 17th century, two large Indian groups inhabited the area—the nomadic Algonquian tribes of the north and the agricultural Iroquoian tribes of the south. For more than 150 years, they prevented permanent settlement of Ontario by Europeans.

Important dates in Ontario
1610 Etienne Brule of France became the first white person to explore the Ontario region.
1613 Samuel de Champlain of France explored the Ottawa River area.
1639 French missionaries founded Fort Sainte Marie.
1648-1649 Indians destroyed the French missions.
1763 The Ontario region became a British possession.
1791 The region became the province of Upper Canada.
1812-1814 American forces invaded Upper Canada during the War of 1812.
1837 A rebellion against British rule broke out in Upper Canada.
1867 Ontario became one of the original four provinces of the Dominion of Canada on July 1.
1883 The world's largest copper-nickel reserves were discovered near Sudbury (now part of Greater Sudbury).
1904 Ontario's automobile industry began in Windsor.
1912 Ontario gained the territory north of the Albany River.
1952 The Western world's largest uranium deposit was discovered at Elliot Lake.
1959 The St. Lawrence Seaway opened.
1964 A huge field of copper, silver, and zinc was discovered near Timmins.
1972 Ontario began a program of free medical and hospital care for the elderly and the poor.
1982 Large gold deposits were discovered at Hemlo, near Marathon.
1985 After 42 years of Progressive Conservative rule, the Liberal Party won control of the provincial government and began a five-year period of Liberal leadership.
2003 Ontario's highest court, the Court of Appeal, upheld a lower court decision to allow same-sex marriage in the province.