Mary Island State Park Campground offers 12 waterfront campsites on a heavily-wooded 12-acre island in the Saint Lawrence River, accessible by boat only (minimum 14' motorized boat required; rentals available at nearby marinas).

The park features boat beaching and mooring near campsites, picnic areas, and foot trails with scenic views of the Canadian shore and shipping channel.

Reservations are required and must be made at least 2 days in advance; the park operates seasonally from Memorial Day weekend through Labor Day.