Lake Simcoe is a lake in Southern Ontario, Canada, the fourth-largest lake wholly in the province, after Lake Nipigon, Lac Seul, and Lake Nipissing. At the time of the first European contact in the 17th century the lake was called Ouentironk ("Beautiful Water") by the Huron natives. It was also known as Lake Toronto until it was renamed by John Graves Simcoe, the first Lieutenant-Governor of Upper Canada, in memory of his father.
The lake is bordered by Simcoe County, Durham Region, and York Region. The city of Barrie is located on Kempenfelt Bay, and Orillia is located at the entrance to Lake Couchiching. The watershed draining into the lake contains a population of roughly half a million people, including the northern portion of the Greater Toronto Area (GTA).
The town of Georgina lies along the entire south shore of Lake Simcoe and consists of smaller residential towns and communities, including Keswick on Cook's Bay, Sutton, Jackson's Point, Pefferlaw, and Udora.