Thompson Island (Massachusetts)

Cathleen Stone Island, also known as Thompson Island, is a 170-acre (69 ha) island in the Dorchester Bay section of Boston Harbor, offshore from downtown Boston, Massachusetts. It is located slightly more than 4 miles (6.4 km) from Boston's Long Wharf via boat, while approximately 1 mile (1.6 km) straight-line distance from Boston's Columbia Point.

The island is managed by the Cathleen Stone Island Outward Bound Education Center, a non-profit education organization. The island is open to visitors on Saturdays and Sundays from Memorial Day through Labor Day; otherwise access is by arrangement only. Cathleen Stone Island is one of the largest, most accessible and ecologically diverse islands in the Boston Harbor Islands National Recreation Area.

The island's highest point is a drumlin that reaches a height of 78 feet (24 m) above sea level. The rest of the island comprises low rolling hills and a salt marsh. The island has a mixed vegetation, including hardwood tree stands, remnant pear and apple orchards, ornamental trees and shrubs, and salt marsh grasses. The island has open meadows, forests, marine wetlands, sumac groves, and a variety of other geological features as well. Amenities include a formal school campus complete with classrooms, dormitories, dining hall, auditoriums, gymnasium, lab space, outdoor challenge courses, and climbing towers. At low tide, a sandbar connects it to the Squantum peninsula, allowing land travel between the two.