Collection consists of three items relating to Saint Helen's Island (Île Sainte-Hélène), located southeast of the Island of Montreal in the Saint Lawrence River. The items relate to the island's military installations, built as defenses for the city of Montreal as a result of the War of 1812 and used as a munitions depot for the British Army and later a garrison, arsenal, and military prison operated by the Canadian Army. Items include a manuscript entitled, "Military Defences. St. Helen's Island - Barons of Longeuil," written by Charles Walkem, August, 1873; "Plan of Isle St. Helens," an undated map on linen paper, with a key pointing out the military installations; and "The Fort, St. Helen's Island," a 4-page pamphlet containing schematics and descriptions of the island's fort as well as a history of the island dating from 1611 to the 1960s. The pamphlet cover photograph features a soldier of the Royal Artillery, Saint Helen's Island Fort, circa 1865. Part of the manuscript document also deals with the hereditary Barony of Longueuil.

Manuscript letter to McTavish signed D.A. Grant, dated St. Helen the 8th June 1792.