Hart Island, sometimes referred to as Hart's Island, is an island in New York City at the western end of Long Island Sound. It is approximately a mile long and one quarter of a mile wide and is located to the northeast of City Island in the Pelham Islands group. The island is the easternmost part of the borough of the Bronx. The island has been used as a Union Civil War prison camp, a psychiatric institution, a tuberculosis sanatorium, potter's field, and a boys' reformatory.