Hardenbergh was one of the founders of the American Fine Arts Society. He was president of the Architectural League of New York from 1901 to 1902 and was a member of the Century, Riding, Grolier, and Church Clubs as well as the National Sculpture Society. He became a member of the American Institute of Architects in 1867 and was made a Fellow in 1877.
| period | name | type |
|---|---|---|
| American Institute of Architects | Fellow |