Southern Ontario is a primary region of the Canadian province of Ontario. It is the most densely populated and southernmost region in Canada, with approximately 13.5 million people, approximately 36% of Canada's population of 37 million. The region lies south of the province's other primary region, Northern Ontario, although the exact northern boundary of Southern Ontario is disputed. However, its core region is situated south of Algonquin Park, the latter being in an area of transition between coniferous forest north of the French and Mattawa Rivers and southern deciduous forest. It covers between 14 and 15% of the province, depending on the inclusion of the Parry Sound and Muskoka districts which also lie in the transitional area between northern and southern forest regions. Southern Ontario differs greatly from Northern Ontario, having a much higher population density, a different climate, and a different culture than its northern counterpart. It is broken into smaller subregions, including Central Ontario, Eastern Ontario, the Golden Horseshoe, and Southwestern Ontario.

Indigenous peoples in Canada are the indigenous peoples within the boundaries of Canada. They comprise the First Nations, Inuit and Métis. Although "Indian" is a term still commonly used in legal documents, the descriptors "Indian" and "Eskimo" have fallen into disuse in Canada, and most consider them to be pejorative. "Aboriginal" as a collective noun is a specific term of art used in some legal documents, including the Constitution Act, 1982, though in some circles that word is also falling into disfavour.