It’s a bit difficult to sort out! The native nations that live in Ontario now aren’t always the ones who lived here before European colonization, and the ones that lived there at the time now often live somewhere else.

Pre-contact (and pre-colonization), all of southern and southwestern Ontario was inhabited by people speaking Iroquoian languages. There were probably Iroquoian-speakers in southeastern Ontario too, as far as modern day Ottawa, and in southwestern Quebec around Montreal. To the north, basically the northern part of the Ottawa River, north of the Nipissing River, the north shores of Lake Huron and Superior, and most of southern Quebec, the land was inhabited by Algonquian-speaking peoples.

Algonquian and Iroquoian languages are totally separate language families and not at all mutually intelligible. They did learn each others’ languages sometimes, and they had plenty of contract through trade and warfare, but Iroquoian-speakers tended to think Algonguian-speakers were culturally very mysterious. Algonquian peoples included the Algonquin, Innu (not the Inuit, who are again a completely different cultural/linguistic group), Odawa, Ojibwe, and Cree, among many others. The Algonquian-speaking peoples who live in Ontario today typically call themselves Anishinaabe.

Iroquoian speakers lived along the St. Lawrence in Ontario, between Georgian Bay and the north shore of Lake Ontario, and between Lake Huron and Lake Erie, as well as to the south of the St. Lawrence and Lake Ontario, around the Finger Lakes in what is now upstate New York. That was probably the Iroquoian homeland and they expanded north of the river/lake afterwards, but pre-Contact. When the French arrived in the 16th century, they found Algonquian peoples in Quebec, but the inhabitants of Stadacona and Hochelaga in the Montreal area were probably Iroquoians. Du to disease, warfare, or maybe just migration, the Iroquoians had disappeared from that area when the French returned in the 17th century.

Iroquoian languages are named after the Iroquois, or Haudenosaunee, who were a confederacy of five Iroquoian-speaking peoples, the Mohawk (Kanien’kehá:ka), Oneida, Onondaga, Cayuga, and Seneca. The five nations had joined together sometime before contact, but it’s not totally clear when - maybe a couple of hundred years earlier, or maybe up to 500 years earlier. (The Tuscarora joined as the sixth nation, but much later in the 18th century.)

Some of the five nations lived or traded north of Lake Ontario. The name “Toronto” might come from a Mohawk word, tkaronto, originally referring to the narrow channel a bit further north between Lake Simcoe and Lake Couchiching where Orillia is today.

Otherwise, the Iroquoian-speakers in what is now southern and southwestern Ontario were not part of the five nations, and were in fact usually at war with the five nations, despite speaking a related language. The French called them Hurons but they called themselves Wendat. The main territory inhabited by the Wendat was at the southern tip of Georgian Bay. Elsewhere in southwestern Ontario there were other groups of Wendat - the Petun, as well as the Attawandaron or “Neutrals”, so called because they preferred to stay out of the Wendat-Iroquois conflict.

The French and other European settlers far to the east on the Atlantic coast really only wanted one thing from the natives - furs, especially beaver pelts. The Wendat around Georgian Bay profited from the fur trade but it also pretty much wiped out the beaver population. In the “Beaver Wars” the Wendat were allied with the French against the Iroquois (and to some extent against the other Wendat). The Iroquois felt threatened because the Wendat now had access to European metal and other goods that the Iroquois didn’t, so Iroquois attacks actually increased after French contact.

French Jesuit priests also lived among the Wendat and tried to convert them (you may be familiar with Ste-Marie-among-the-Hurons, near Midland). But they also brought diseases, so the combination of Christianization and disease ended up massively destabilizing Wendat society.

Eventually the Iroquois destroyed the Wendat communities around Georgian Bay. Some of the Wendat either joined the Iroquois, or joined the Petun and Neutrals in southwestern Ontario, but the Iroquois drove them from there as well. By around 1660, there were actually no permanent settlements in southern Ontario at all. The Iroquois hunted there and traded with the Algonquian peoples to the north but otherwise the area was depopulated.

In the 18th century the British conquered New France and started settling in French territories. Following the American Revolution and the War of 1812, several native nations had allied with the British against the Americans, and the British began resettling their allies in the otherwise empty territory in southern Ontario. This is why there is a mixture of Iroquoian and Algonquian languages among the native nations that currently live in southern Ontario.

The Mississaugas of the Credit, Chippewas of the Thames, and Chippewas of Kettle and Stoney Point, for example, are Algonquian-speaking nations who were resettled in Ontario in the 18th and 19th centuries. Other Algonquian-speakers were resettled from further away - the Lenape from Delaware, who speak the Algonquian Munsee language, now live in southwestern Ontario.

But the Six Nations of the Grand River are Haudenosaunee resettled from upstate New York on the “Haldimand Tract” in southern Ontario - you may be familiar with the recent “1492 Land Back Lane” protests against housing developments on the Haldimand Tract.

There are still some Wendat communities in Ontario, but they were mostly resettled too, in Michigan and as far south as Kansas and Oklahoma.

As you can tell from my flair this is certainly the wrong part of the world and the wrong time period for me, but I live in southern Ontario too, so this is something I’ve always been interested in (I was actually planning on studying this in grad school before I switched to medieval history). My elementary school was named after one of the Jesuit missionaries to the Wendat and we even went on a school trip to Ste-Marie. Here in London we have the Museum of Ontario Archaeology, which is a pre-contact Attawandaron village, and a bit further west there is a memorial to Tecumseh, the Shawnee (Algonquian-speaking) ally of the British who was killed at the Battle of the Thames in 1813.

So, in short, pre-Contact in the 16th aand 17th centuries, southern Ontario was inhabited by the Wendat and Haudenosaunee, who spoke Iroquoian languages, but they interacted with nearby speakers of the separate Algonquian language family. Post-Contact in the 18th and 19th centuries, several Iroquoian and Algonquian-speaking nations were resettled in Ontario.

Sources:

Bruce G. Trigger, “The original Iroquoians: Huron, Petun, and Neutral”, in Aboriginal Ontario: Historical Perspectives on the First Nations, ed. Edward S. Rogers, Donald B. Smith (1994)

Bruce G. Trigger, The Children of Aataentsic: A History of the Huron People to 1660 (1976)

Marit K. Munson and Susan M. Jamieson, eds., Before Ontario: The Archaeology of a Province (2013)

Land acknowledgements from universities in the area (Toronto, Laurier, Waterloo, Western, etc.) and other organizations (the Stratford Festival for example) are another good way to find out who lives here now.

native-land.ca also shows which First Nations used to live here, and which ones live here now (although it doesn’t really distinguish between them so it can be kind of confusing).