Before the arrival of Europeans the Ontario region was inhabited by several Algonquian (Ojibwa, Cree, and Algonquin) and Iroquoian (Iroquois, Huron, Petun, Neutral, Erie, and Susquehannock) tribes. Étienne Brulé explored southern Ontario in 1610–12. Henry Hudson sailed into Hudson Bay in 1611 and claimed the region for England. A few years later Samuel de Champlain reached (1615) the eastern shores of Lake Huron, and French explorers, missionaries, and trappers had established posts at several points. However, settlement was long hindered by the presence of the Iroquois.
In the late 17th cent. the British established trading posts in the Hudson Bay area, and the Anglo-French struggle for control of Ontario began. The conflict was resolved by the Treaty of Paris of 1763, which gave Great Britain all of France's mainland North American territory. In 1774 the British merged Ontario with Quebec, which had a predominantly French culture. When many pro-British Loyalists migrated to Ontario after the American Revolution, the desire for institutions and a government separate from those of Quebec grew. The Constitutional Act of 1791 split Quebec into Lower Canada (present-day Quebec) and Upper Canada (present-day Ontario), with the Ottawa River as the dividing line.
During the War of 1812, Americans raided Upper Canada and burned Toronto (1813). After the war many English, Scottish, and Irish settlers came to the colony. Conflict developed between the conservative, aristocratic governing group (known as the Family Compact) and the reformers and radicals led by William Lyon Mackenzie. The radicals staged an armed uprising in 1837 but were easily suppressed. However, the rebellion occurred at the same time as a revolt in Lower Canada, and the British government dispatched Lord Durham (see Durham, John George Lambton, 1st earl of) to study the situation in the North American colonies. He recommended the reunion of the two colonies (to place the French of Quebec in a minority) and the granting of self-government.
Accordingly, Upper and Lower Canada were joined in 1841 and became known, respectively, as Canada West and Canada East. Parliamentary self-government was not granted until 1849. However, conflict between French and English made the united province unworkable, and in 1867, when the confederation of Canada was formed, Ontario and Quebec became separate provinces. With the construction of the transcontinental railroad in the 1880s, settlement increased in western Canada, and Ontario's commerce and industry flourished. The exploitation of minerals in the Canadian Shield region began in the early 20th cent. From the 1960s, many businesses that left Quebec because of agitation against anglophone economic domination there relocated around Toronto, shifting the balance of Canadian business and financial power decisively to Ontario.
The main political parties in Ontario are the Liberals, who held power during the late 19th cent. and for a few terms during the 20th cent.; the Progressive Conservatives, who governed from 1905 to 1985 (except in 1919–23 and 1934–43); and the New Democrats, a democratic socialist party, who controlled the government from 1990 to 1995. Elections in 1995 brought Michael Harris and the Progressive Conservatives to power; after four years of cuts in social spending, Harris became (1999) the first Ontario premier to secure a second term in three decades. He resigned as premier in Apr., 2002, and was succeeded by Ernie Eves.
In 2003 the Liberals, led by Dalton McGuinty, won at the polls, and formed their first provincial government since 1990. They won again in 2007 and, with a plurality, in 2011. Liberal Kathleen Wynne succeeded McGuinty as premier in 2013, becoming the first woman to lead the province and Canada's first openly gay provincial premier.
Ontario sends 24 senators and 99 representatives to the national parliament.