Adelphi University Adelphi University, Garden City, New York, private, coeducational institution of higher learning in Garden City, New York, U.S. Adelphi is a liberal arts college serving Long Island, with branch campuses in Manhattan and Huntington. It offers a range of bachelor’s and master’s degree programs in business, nursing, social work, and the arts and sciences. Doctorate degrees are offered in nursing, education, social work, and psychology. Total enrollment is about 7,000.