The John M. O'Connor papers contain 350 letters, 15 financial records, 7 legal documents, and several lists, clippings, and the lyrics to a song, spanning 1810-1826. The correspondence is almost entirely incoming and the majority dates to the period from 1815 to 1824. Approximately 20 of the letters relate to the War of 1812; some discuss official army matters, such as supplies and troops, while others concern popular opinion of the war (June 26, 1813: "The public do not appear to be satisfied with the military acquirements of the Commander in chief, and not a few are so daring as to stigmatize his operations as being tardy & imbecile"). A series of letters in September and October 1812 relate to the death of O'Connor's mother, Margaret.
Correspondence in 1815-1816 mentions and documents the chain of events arising from the feud between O'Connor and Major General George Izard, including O'Connor's court martial and subsequent leave of absence, and his attempts to regain his position and good standing in the army. Slightly later correspondence documents O'Connor's translation of Gay de Vernon's Treatise on the Science of War and Fortifications, and includes a letter from O'Connor to Secretary of War, John C. Calhoun, encouraging him to request more copies of the work in order to ensure the success of the project (March 4, 1818). Approximately 15 letters from this period were written in French.
The majority of the material, particularly later in the collection, relates to national politics and political factions in New York State. On October 12, 1818, William H. Crawford, whom O'Connor would later back in the presidential election of 1824, wrote to O'Connor concerning a visit to the South, including observations on the failure of crops, family news, and French politics. On February 18, 1820, James Taylor provided a long account of the Missouri Compromise to O'Connor, and commented that "I am constrained to believe that the spirit of intolerance & oppression towards the black man, and the determination to perpetuate his bondage…are daily gaining ground in the Southern & Southeastern United States." Letters of November 1823 concern the presidential election of 1824 and New York politics.
Also of interest are letters from O'Connor's sister, Eliza, who seems to have been a governess or lady's companion in Middletown, Pennsylvania, but left because of dissatisfaction with the position: "You say that I was placed with the most respectable family in Middletown and all my wants were provided for, and I was at once raised to a respectable and enviable situation, as to their respectability no one will dispute it, as to my situation being enviable, I do not know how excepting I was independent of them, the want of relations will never be compensated to me by strangers" (August 25, 1820). Many letters throughout the collection also document O'Connor's interest in trading stocks and bonds. Letters from his agent, Thomas Hutchison, show his interest in bank bonds and provide advice and information on securities trading.
Several of the documents in the collection relate to the military, including 1814 General Orders, several financial records, and two certificates. Also included are several bonds, a bill of lading, and lists relating to O'Connor's translation work.