The Syracuse-Onondaga Salt series contain materials dating from 1839 to 2012 that are similar material to the location series above, but due to the large quantity of information on these topics, as well as the fact that many of these companies are or were national or even international, have warranted their own series. Each series is organized by subject, including business, correspondence, ephemera, images, publications, postcards, and films.

It must be noted that Syracuse-Onondaga Salt does not refer to a specific company, but rather the area around the Onondaga Creek Valley where there are large natural salt deposits and brine springs. In 1788 the area around the Onondaga Lake was designated by the New York State legislature as the Onondaga Salt Springs Reservation. Salt production and sale in this area was regulated by the state in order to prevent monopolies and to generate state revenue. This area was important enough that Carol Litchfield considered it a significant area of research and kept items regarding Syracuse-Onondaga area salt together. Notable companies in the area include: The Onondaga Coarse Salt Association, The American Dairy Salt Company, and The Salt Company of Onondaga.