Thousand Islands National Park, formerly known as the St. Lawrence Islands National Park, is a Canadian National Park located on the 1000 Islands Parkway in the Thousand Islands Region of the Saint Lawrence River. The islands are actually the worn-down tops of ancient mountains. This region, the Frontenac Axis, connects the Canadian Shield from Algonquin Park in Ontario to the Adirondack Mountains in New York.

The Thousand Islands constitute a North American archipelago of 1,864 islands that straddles the Canada–US border in the Saint Lawrence River as it emerges from the northeast corner of Lake Ontario. They stretch for about 50 miles (80 km) downstream from Kingston, Ontario. The Canadian islands are in the province of Ontario and the U.S. islands in the state of New York.