The collection consists mostly of Tallmadge's papers relating to the Revolutionary War, including correspondence with George Washington during his involvement in the secret service, a photostat of his code used then, letters to David Humphreys, Timothy Pickering, and William B. Sprague, and letters and newspaper extracts dealing with the Major Andre affair. Also present are family letters, a deed signed by William Floyd (a signer of the Declaration of Independence), documents signed by Alexander Hamilton, Tallmadge's will, a diary of his journey to Marietta in 1795, photographs of family portraits, and miscellaneous material.