The Athenæum houses an outstanding collection of documents and artifacts relating to local history. It also preserves what is undoubtedly the finest collection in the state of materials relating to the history of New Hampshire's only major seaport. The Sawtelle Reading Room serves as a gallery to display highlights of the maritime collection, including paintings of local ships, a series of portraits of ship captains, merchants, and naval officers, and the gilt figurehead from the schooner Alcea. A jewel of the collection is the plank-on-frame model of the ship America, built in Portsmouth for the Royal Navy in 1749. It is the oldest surviving model of an American-built ship. The Athenæum displays more than forty half-hull builder's models of Piscataqua-built vessels, and the oldest surviving measured drawing of an American ship, the Elizabeth , launched from a tributary of the Piscataqua in 1752.

Of even greater importance than the impressive visual collections are the superb archival collections. These include the Customs House records for the port of Portsmouth during the American Revolution and the extraordinarily detailed records of the New Hampshire Fire & Marine Insurance Company, which insured hundreds of voyages during its twenty years of operation between 1803 and 1823. In all, the library holds approximately 400 lineal feet of archival materials and more than 8,000 historic photographs documenting the early history of the port city. These materials along with the 40,000 volume library are open and available to researchers and the general public free of charge three days per week. The historic Sawtelle Reading Room is open free of charge for tours one day per week, and the Athenæum's Randall Gallery, which hosts three exhibitions every year on themes of local art and history, is open at no cost three days per week. Nearly all of the Athenæum's historical, literary, musical, and scientific programs are offered to the general public free of charge.