Frobisher's papers comprise a letterbook of the North-West Co. containing copies of letters written by Frobisher from April 1787 to October 1788, two original letters to Simon McTavish, 1796, and one from him, 1787, business and legal documents, largely concerning the estate of James McGill, 1810-1834, and a diary, 1806-1810, mostly a record of where he dined.

The collection contains business correspondence, including letters to William Grant and Grant, Campion & Co. from Brickwood, Pattle, & Co., 1792-1793, and letters from Brickwood & Daniell, John Blackwood, and McTavish, Fraser and Co., 1799-1800. There is also a bound letter book for Grant and Laframboise, Montreal, 1800-1801 with additional loose leaves of letter copies dating between 1798 and 1800.