[5] The island was once mainly the home territory of the Chappaquiddick band of the Wampanoag people, and remained exclusively theirs well into the nineteenth century.

The Trustees of Reservations, a non-profit conservation organization, owns and manages nearly 1,000 acres (405 ha) of land from the southeastern point,[8] Wasque, to Cape Poge, at the northeast.

Chappaquiddick is mainly defined by its diverse land and water ecologies with expansive salt marshes, ponds, red cedar woods, grassy meadows, and coastal wildlife including sandpipers, piping plovers, blue heron, osprey, and oysters.

Between 2007 and 2013, approximately 40 acres (16 ha) of land were lost at Wasque,[10] where currents eroded bluffs, swallowed Swan Pond, damaged shoreline trails, and threatened a residence.

[19] Oversand access is possible with four-wheel drive vehicles and on foot on the south shore when the islands are connected and conditions permit.

Chappaquiddick Island gained international attention on July 19, 1969, when the body of Mary Jo Kopechne was discovered inside an overturned Oldsmobile 88 off Dike Bridge in Poucha Pond.

Senator Ted Kennedy, who claimed that he had taken a wrong turn and accidentally driven it off a bridge late the previous night.

[20] A January 1970 judicial inquest into Kopechne's death found that Kennedy's turn toward the bridge was intentional, and he operated his car in a manner "at least negligent and possibly reckless".