Horse Island, at 17 acres (69,000 m²), is the largest of the Thimble Islands off Stony Creek, a section of Branford, Connecticut. It is owned by Yale University and is maintained as an ecological laboratory by Yale's Peabody Museum of Natural History. It was purchased and donated to the university in 1971 as a convenient addition to the Yale Coastal Field Station in nearby Guilford, which has its own dock and boats.