The Benjamin Tallmadge Collection documents the personal life and professional career of Colonel Benjamin Tallmadge through his correspondence as well as his legal, financial, and personal papers.  An army officer, chief intelligence officer, and organizer of the Culper spy ring during the Revolutionary War, Tallmadge became a businessman and U.S. Representative from Connecticut in Congress after the war.

The collection contains Tallmadge's duplicate original letters to George Washington concerning military operations and Tallmadge's operations of the secret service during the Revolutionary War.  These letters record  not only detailed summaries of battles, movements of troops, and requests for provisions, but also the activities of spies and communications of their intelligence.  Many of the letters are written in cipher.  Also included are two original letters from Washington to Tallmadge concerning military administration. 

The letters also record Tallmadge's business activities after the war, especially in his correspondence with his son-in-law, John Paine Cushman, a lawyer in New York and, from 1817-1819, U. S. Representative of New York in Congress, whose advice and assistance Tallmadge frequently sought for his financial transactions.

In addition, legal documents, accounts, and bills and receipts illuminate Tallmadge's business ventures, especially his purchases and sales of land in Vermont, New York, Massachusetts, and Ohio, with references to the Ohio Company and Western Reserve.  Other items include accounts for Tallmadge's store in Litchfield, Connecticut; receipts documenting his investment in privateering ships; and indentures of African Americans and bills of sale of enslaved people. 

Moreover, his letters to Cushman reveal their opinions on national politics and government, especially during Cushman's own service in Congress.  Meanwhile, his letters to his daughter, Maria (Tallmadge) Cushman, document the religious revival movement in New England, in which Tallmadge took great interest, describing the activities of such revivalist preachers as Lyman Beecher, Asahel Nettleton, and Nathan Beman.  These letters also provide insight into the social and personal activities of the Tallmadge and Cushman families in Litchfield and elsewhere.  Occasionally, the letters are appended by notes to Maria from Tallmadge's second wife, Maria (Hallett) Tallmadge.

The collection also contains correspondence and business papers of Tallmadge's son, Frederick Augustus Tallmadge, which primarily concern Frederick Tallmadge's publication of his father's memoirs.