Fort Lennox National Historic Site occupies all of Île-aux-Noix, a small island in the Richelieu River near Saint-Paul-de-l'Île-aux-Noix, Quebec.

The fortification, built between 1819 and 1829, reflects the island's long strategic role guarding the Hudson-Champlain-Richelieu corridor against invasion, seeing French, American, and British military presence from 1759 through the 1870s.

The site includes a picnic area among its visitor amenities, making it a viable day-use destination. Picnics are permitted on the island grounds, and visitors are advised to bring their own food and water, as provisions on the island are limited.

Access to the island is by ferry from the mainland.