 Duncan was a Fellow of the Royal Astronomical Society and the American Astronomical Society (as Secretary of the later from 1936 to 1939), as well as a member of the International Astronomical Union, and since 1938 the American Association for the Advancement of Science, the American Academy of Arts and Sciences and numerous other scientific organizations.The asteroid , discovered on 18 February 1966 at the Goethe Link Observatory, was named after him.John Charles Duncan was married to Katharine Armington Bullard since 1906, with whom he had a daughter.