The Augustus Garrett Letterbooks consist of two bound volumes of copies of outgoing (and occasional incoming) letters of Augustus Garrett. The first volume (280 pp.) spans the period from October 29, 1843, through January 2, 1845; the second (214 pp.) from January 3 through August 19, 1845. The correspondence is concerned almost entirely with financial and other business matters. The largest single portion (perhaps a quarter of the letters) is addressed to John F. Seaman, and deals with insurance and financial transactions. The correspondence with Seaman also includes letters of introduction on behalf of Garrett's Illinois business associates.
The volumes also include correspondence with John Brower, President, and J. W. Savage, Vice President, of the National Fire Insurance Company of New York, dealing with policies written by Garrett for the Company; the firm of Garrett, Seaman, and Stearns, of Dixon, Illinois, concerning merchandise orders and shipments; J. R. Malony, of New York City, dealing with merchandise orders, insurance, and Garrett's observations on Chicago politics; Illinois Governor Thomas Ford and Congressman John Wentworth, concerning political appointments and pardons; and J. A. Noonan, of Milwaukee, Wisconsin, concerning Noonan's prospects as an agent for the National Fire Insurance Company, and the coverage of Garrett's affairs in a Milwaukee newspaper apparently edited by Noonan.
Other occasional correspondents include Garrett's insurance clients, and suppliers of goods and services with whom he corresponded in his capacity as Mayor of Chicago.