Since McCormick was so often absent from Chicago on business, voluminous correspondence was necessary. He communicated in great detail with company officials William S. McCormick and his successor, Charles A. Spring Jr., each of whom wrote McCormick concerning personal and business matters, patents, agreements, sales, agents, and investments; while his brother Leander's letters refer to design, operation, and patents. Other correspondents include foreign agents after 1851; traveling agents who moved throughout the Midwest and the East after 1845; and small-town implement dealers and general agents who came to be the eyes and ears of the company, as well as salesmen for the McCormick machines. With improvements in the reaper and introduction of the mower, self rake, harvester, and binder, patents cases and manufacturing rivalries generated much of the correspondence. Included are letters and agreements relating to patentees and manufacturers, as well as those who advised and represented McCormick in business and legal matters.
Presbyterian Church affairs were a dominant personal interest and the correspondence with churchmen reflects growth of several Presbyterian churches in Chicago, church dissension prior to the Civil War, and controversies between conservative and radical theology. To advance his Old School point of view McCormick endowed the Presbyterian Theological Seminary of the Northwest at Chicago, now called the McCormick Theological Seminary; fought to maintain conservative instruction; and contributed to its buildings and operation. Other schools of which he particularly approved were recipients of his support. McCormick corresponded with and supported the evangelism of Dwight L. Moody, and established a family tradition of consistent aid to the Young Men's Christian Association. Appeals for financial assistance increased after the Civil War when a flood of pleas came from their family home state of Virginia and the South. McCormick responded to numerous individuals and letters reveal his concern for impoverished churches and the welfare of blacks, with substantial contributions especially to the Southern Aid Society.
In politics McCormick was a Democrat, taking an active though somewhat sporadic interest in national conventions and election campaigns. Being opposed to abolition and secession, his correspondence prior to the Civil War emphasizes his hope that both his party and his church could help to prevent a break between the states. Much of his political correspondence relates to his service as chairman of the Democratic State Central Committee in Illinois.
McCormick's investments were varied and included speculation in railroads, mineral lands, and other properties. Correspondents include lawyers and financiers in New York. Major interests include the Union Pacific Railroad Company, the Southern Railroad Association, the Tehuantepec Inter-Ocean Railroad Company, and rail construction in Iowa, Nebraska, and elsewhere. Investments in the Montana Mineral Land and Mining Company and Arizona properties, and abortive attempts to obtain gold at the Dorn mine in South Carolina and silver at the Little Chief mine in Colorado prompted much correspondence. Other investment was in the Mississippi Valley Society of London formed to encourage European capital and immigrants to seek the Midwest; and foreign interests such as the American Exchange in Europe, Ltd.
Personal concerns are documented throughout the collection. Letters with family members and business and investment affairs also include comments on family and social affairs. After McCormick's death, the papers chiefly concern the trusts created by his will and the administration of his estate.
