John R. Williams' Papers are housed at the Burton Collection at the Detroit Public Library. From the Library's site:
Abstract: [Papers are] Principally mercantile records and correspondence relating to the fur trade and Great Lakes shipping; also political and governmental subjects; personal correspondence and bills; property leases, sales and purchases... War of 1812.
Williams was born in Detroit (Mich.) on May 4, 1782. In 1796 he served under Gen. Wilkinson in 1796 at Fort Marsac (Tenn.) [Note: Probably Fort Massac* in IL]. In the War of 1812 he served as Captain of the artillery and was taken prisoner when Detroit fell.