The incoming correspondence contains numerous enclosures documenting William du Pont's activities. There are financial statements (E.I. du Pont de Nemours and Company, Atlantic Mining Company, Hercules Powder Company, United States Fidelity and Guarantee Company of Baltimore, Mercantile Trust and Deposit Company of Baltimore, Wilmington Country Club, Delaware State Fair, Inc., English Jersey Cattle Society (London), National Horse Show Association of America, Ltd., Sulgrave Institution of the United States, United Light and Railways Company, and Ferris Industrial School of New Castle County); prospectuses issued by various companies, banks, and investment firms; by-laws and/or articles of incorporation (Percheron Horse Society, Ball Island Gun Club, Atlantic Yacht Club, American Junior Naval & Marine Scout, Inc., Delaware State Fair., Inc.); informational leaflets of the Horse Association of America (over fifty issues); bulletins of the National Parks Association, 1922-1923 (Nos. 24, 25, 28, 29, 31, 34, 35), catalogs and advertisements of agricultural products, domestic goods, clothing, wine, etc.; horse and cattle show programs; various printed materials (Association of American Horse Shows, Inc., North Jersey Agricultural Society, Percheron Society of America, Eastern States Exposition [Springfield, Massachusetts], Kentucky State Fair Horse Show, Graham Scientific Breeding School [Kansas City, Missouri], Southern Railroad (United States), Association Against the Prohibition Amendment, Philadelphia Riders and Drivers Association, clubs, etc.); blueprints and drawings (maps of estate in Georgia and William du Pont's land in Virginia near Montpelier purchased by Southern Railway; plan of properties near Bellevue; arrangement of electrical lighting plant in power house at Montpelier, 1917); photographs of horses, dogs, prize items, and buildings of mansions offered for sale; estate auction announcements; descriptive circulars for books printed by Charles Scribner's Sons, J. B. Lippincott Company, and other publishers, predominantly on American history and horse breeding; newspaper clippings; restaurant menus; Christmas cards; bills of lading; receipts; business cards; and copies of outgoing letters related to the subject.

Individual items of note include a short history of the American-Russian enterprise Lied Incorporated organized by Jonas Lied in 1918; genealogy of Annie Rogers du Pont on her mother's side (letter from law offices of Ward, Gray, and Neary, March 10, 1920, shows her distant family tie to the American painter Mary Cassatt); a short biography of the painter Charles Lewis Fox (1854-1927), written by his friend and schoolmate John R. Freeman, 1927; a proposed issue of the Livestock Pictorial, mid-month rotogravure section of Syndicated Farm Papers (enclosure with the letter of the publisher P. C. Long, 1925); an outline of William du Pont's presentation at a horse show "Scenario. Thirty Years of Hackney Breeding. By William du Pont" (Miscellaneous enclosures).

A number of letters collected in this subseries are addressed to members of William du Pont's immediate family: his father Henry du Pont, his wife Annie Rogers du Pont, daughter Marion du Pont (Somerville), and son William du Pont Jr.; and to his secretaries Chas K. Lennig, E. C. McCune, G. H. Montgomery, Earl E. Edinger, and F. M. Modena.

The subseries is organized chronologically by year (by parts of the year for 1917-1919, according to the original arrangement) and subdivided alphabetically by the name of the correspondent. Enclosures were kept with the letters with the exception of the oversize materials. Loose enclosures which were kept with the correspondence files were placed in Miscellaneous Enclosures folder.