The St. Lawrence Iroquoians are a prehistoric First Nations/Native American indigenous people who live from the 14th century until about 1580 CE along the shores of the St. Lawrence River in present-day Quebec and Ontario, Canada, and New York State, United States.

They spoke Laurentian languages, a branch of the Iroquoian family.

It is likely they disappeared because of late 16th century warfare by the Mohawk nation of the Haudenosaunee, who wanted to control fur trade in the valley.

Knowledge about the St. Lawrence Iroquoians has been constructed from the studies of surviving oral accounts of the historical past from the current Native people, writings of the French explorer Jacques Cartier, earlier histories, and anthropologists' and other scholars' work with archeological and linguistic studies since the 1950s Archeological evidence has established this was a people distinct from the Five Nations of the Haudenosaunee and the Huron.

Recent archeological finds suggest there may have been distinctly separate groups among the St. Lawrence Iroquoians as well.