Copies of Irvine's correspondence, 1781-1783, while he was commanding general at Fort Pitt. These transcripts were made by Butterfield and were sent to Draper after the publication of Butterfield's book. These letters were neither included in that publication nor indexed. Although most of the letters deal with border defense and the great majority of the writers were military officers, there are more than fifteen personal letters written by Irvine to his wife; these pertain to family health, business affairs, servants, and the children's education.

Writers of letters to Irvine were Joseph Beckett, Thomas Buchanan, Richard Butler, William Butler, John Byers, Charles Campbell, Thomas Clingman, Joshua Davidson, John David, David Duncan, M. Everly, Charles Foreman, Hugh Goudy, Robert Hanna, Peter Harkcom, Christopher Hays, Moses Hazen, Michael Huffnagle, John Irwin, and Thomas Irwin. Also included were Richard Johnson, M. Lacassagne, William Love, Alexander McClean, William McCleary, David McKee, John Marshall, John Montgomery, Thomas Moore, William Neill, James Potter, John Pumroy, Henry Rhoads, Matthew Ritchie, John Rose (Baron Rosenthal), Arthur St. Clair, Samuel Sample, David Shepherd, Devereaux Smith, Dennis Springer, William Trent, George Vallandigham, David Vance, Samuel Wilson, and Antoine Felix Wuibert. A few letters written by Irvine were addressed to Duncan, Huffnagle, McCleary, Smith, and Trent. Bound among the copies is one original letter (May 1782) written to Irvine by William Crawford reporting on his difficulties with the volunteers in crossing the Ohio River.