Letterbook, 1814-1827, containing copies of Forsyth's outgoing letters to government, military, and business associates. His early letters deal with trade with tribes in Illinois and adjacent areas; among the many references to the War of 1812 are an account of the death of Tecumseh and a discussion of Forsyth's claims for his property losses. Amid the 1817 letters are biographical sketches of Tecumseh and the Potawatomi warrior known as the Main Poque. Descriptions of Forsyth's travels as Indian agent through northern Illinois and up the Mississippi to Prairie du Chien and Fort Snelling are found in letters, 1818-1820. During the 1820s numerous topics occur: intertribal warfare of the Sauk and Fox tribe against the Sioux (1822); Forsyth's protest against the evacuation of Fort Dearborn (1823); the rising tension occasioned by white hunters and lead miners invading Indian lands in northwestern Illinois and southwestern Wisconsin and the resultant harassment of the Indian owners; Forsyth's attempts to discourage white squatters from hunting and trapping on Indian territory; the treaty of Prairie du Chien (1825); the Winnebago unrest of 1826-1827; and Black Hawk's discontent and his desire to war on the Sioux (1827).

Scattered throughout the volume are reports on British policies and influence over the Indians and commentaries on the evils caused by overabundant distribution of whiskey to the Indians by traders. Forsyth's major correspondents were William Clark; Ninian Edwards; Benjamin Howard; Thomas L. McKenney; and successive Secretaries of War William Eustis, John C. Calhoun, and James Barbour, but occasional letters were also addressed to Lewis Cass, Rufus Easton, James Latham, William Lee, Alexander McNair, John Scott, Lawrence Taliaferro, Thomas T. Tucker, and A.P. Vanmatre.

Among the many prominent Indian leaders discussed are the Potawatomi Black Partridge and Gomo; the Sauk Keokuk; the Shawnee Prophet (brother of Tecumseh); the Sioux chiefs Red Wing, Little Crow (d. 1824), and Wabasha; and the Winnebago Prophet and Tomah (known as Thomas Carron). Fur traders mentioned include Maurice Blondeau, Nicolas Boilvin, George Davenport, Robert Dickson, Amos Farrar, Antoine Gautier (Gauthier, Gothier), Henry Gratiot, and Joseph Rolette. Most of the letters, 1814-1818, were published by t and Gomo; the Sauk Keokuk; the Shawnee Prophet (brother of Tecumseh); the Sioux chiefs Red Wing, Little Crow (d. 1824), and Wabasha; and the Winnebago Prophet and Tomah (known as Thomas Carron). Fur traders mentioned include Maurice Blondeau, Nicolas Boilvin, George Davenport, Robert Dickson, Amos Farrar, Antoine Gautier (Gauthier, Gothier), Henry Gratiot, and Joseph Rolette. Most of the letters, 1814-1818, were published by the Society in Wisconsin Historical Collections, XI (1888), 316-355.