- Harrison Hagans Account Books, 1836/18581
- Harry W. Sanders Papers, 1913/19811
- Hartley A. Soule Papers, 1945/19721
- Henry Brooke Letter and Flyer, 1893/19091
- Henry J. Kelley Papers, 1948/19881
- Henry M. Morris Papers,, 1937/19991
- Henry Morgan Jacocks Papers, 1898/19191
- Hermann Fricke Manuscript, 19321
- Howard S. Avery Papers, 1913/19961
- Hugh P. and Ethel C. Kelly Collection, 20001
- Huron, Ohio, Railroad Construction Photographs, 1912/19371
- Irving J. Good Papers, 1925/20041
- Ivory-Billed Woodpecker1
- J. A. Burke, Jr., Collection, 1936/19471
- J. V. Paterson Notebook, 18911