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

Each site features picnic tables, water access for beaching/mooring boats, and spectacular views of the Canadian shore and shipping channel, making it ideal for paddlers and anglers seeking seclusion.

The park operates seasonally (late May through early September) with amenities including hot showers, restrooms, and a water fillup station.