 Iselin was a trustee of the Metropolitan Museum of Art and a member of the Order of the Knights of Malta, the Downtown Association, the Luncheon Club of Wall Street, the Knickerbocker Club, the Metropolitan Club, the Union Club, the Piping Rock Club, the Turf and Field Club, the Riding Club, the New York Yacht Club, the Larchmont Yacht Club, the New Rochelle Yacht Club, and the Genesee Valley Club of Rochester.His widow died in her sleep on 1931.Iselin died on January 29, 1935 at his home, 820 Park Avenue in New York City.