The Loyalists gave the province its Anglo-Saxon character, which was reinforced by waves of immigration from the United States and, during the 19th and early 20th centuries, from the British Isles. Beginning in the late 19th century there was localized immigration from Québec into eastern and northeastern Ontario, creating a French-language fringe along the province's frontiers. Although northern Ontario received some overseas immigration in the early 1900s, it was not until after 1945 that immigration from continental Europe, the West Indies and East Asia had a discernible impact on the main populated areas of the province.

Ontario was settled mostly by farmers, but in the mid-19th century, the population was channelling into the cities. By the First World War, Ontario was predominantly urban. In 2011, 86 per cent of the population was urban. By comparison, 160 years earlier, in 1851, the figures were reversed: 86 per cent of Ontario’s population was rural. Ontario’s total population is about 13.5 million (2012), making it the most populated province in the country.