The Mary Flagler Cary Arboretum is a nonprofit arboretum located on U.S. Route 44 near Millbrook, New York. It is operated by the Cary Institute of Ecosystem Studies, and open to the public without an admission fee. The arboretum was established by Mary Flagler Cary (1901–1967), a granddaughter of Henry Morrison Flagler and heir to part of the Standard Oil fortune, and her husband Melbert Cary. After her husband's death in 1941, Mrs. Cary maintained the property, with a special interest in its maples. Following her death in 1967, she left the estate to a trust. In 1971 its trustees asked the New York Botanical Garden to oversee the property, which was then named the Mary Flagler Cary Arboretum. In the 1980s, the Institute for Ecosystem Studies was founded, and in the 1990s it became an independent, nonprofit corporation. In 2008, the Institute adopted a new name, the Cary Institute of Ecosystem Studies