Mary Island State Park comprises 12 heavily-wooded acres with steep rocky outcroppings. Twelve waterfront campsites are scattered throughout the park, offering seclusion and spectacular views of the Canadian shore or the shipping channel. Boats may be beached or moored near campsites. The park has a picnic area and several foot trails.
Access is by boat only from either Grass Point State Park (4 miles over water), or Keewaydin State Park, which is 2 miles from the island.
