John Greenwood was born in Boston, Massachusetts, on May 17, 1760, the son of Isaac Greenwood, a dentist, and his wife, Mary. From 1773 to 1775, he worked as an apprentice cabinetmaker under his uncle, Thales Greenwood of Portland, Maine, and he returned to Boston in early 1775. Greenwood enlisted as a fifer in Captain Theodore Bliss's company of the 26th Massachusetts Regiment on May 3, 1775, and he served for around 20 months. After 1777, he sailed in the Caribbean on vessels directed to intercept British ships. The British captured him on several occasions, though he escaped from prison each time. From February 13, 1778-May 13, 1778, he served as a fifer with John Hinkley's company of Lieutenant Colonel Symmes's guard detachment in Boston. After the war, Greenwood moved to New York, where he served as George Washington's dentist and influenced contemporary dental practices. He and his wife, Elizabeth Weaver, were married in 1788 and had 4 surviving children: Jane Weaver (1789-1861), Isaac John (1795-1865), Clark (1797-1838), and John William (1804-1838). John Greenwood died on November 16, 1819.