The William du Pont papers primarily encompass the years of his active business life from the early 1880s to his death in 1928. There are also some papers from his early life and after his death. This includes some early personal correspondence from his school years, agreements regarding tracts of land which constituted his property in Brandywine and Christiana Hundreds in New Castle County, Delaware, and business papers related to the companies whose activities started before William du Pont's involvement or lasted after his death. There is also a gap in his general correspondence and for invoices and receipts for the first decade of the twentieth century when the family lived at Montpelier, Virginia.

Series I., Subseries C. contains correspondence with lawyers and family members concerning William du Pont's inheritance from his parents and the estate of his late wife Annie Rogers du Pont. A draft of William du Pont's last will is stored with miscellaneous financial papers in Series VI.

The majority of business-related correspondence of William du Pont is in Series II: General Correspondence. The series covers the entire period of du Pont's business life, except for the years from 1902 to 1912, when his main residence was at Montpelier, Virginia. Correspondence reflects his major activities: involvement with powder and dynamite companies; investments in railroads, transportation, utilities, and banking enterprises; membership in horse and cattle breeding societies and clubs, horse show organizations, and hunting clubs; contacts with horse breeders and dealers; relations with publishers of periodicals and books on horse and cattle breeding and races (subscription, advertising, photograph contribution); and construction, renovations, and repairs at personal properties and business buildings. Many letters pertain to charity requests and donations.

William du Pont's business contacts were both local and national. Among his Delaware, Virginia, and Georgia correspondents are contractors, farm, and construction suppliers, utility companies, personal secretaries, farm managers, and employees (Robert H. Blain, J. S. Burtsfield, Hugh B. Craig, S. Sharp Craig, Edmund C. McCune, Earl E. Edinger, F. M. Modena). His involvement with the horse industry is documented in correspondence with organizations such as the American Jersey Cattle Club, Percheron Society of America, the National Horse Show Association of America, Advanced Agricultural Publishing Company, The Agricultural Press, Inc., and the British publishing house Welbecson Press, Ltd. His contacts with horse breeders and dealers included Lehman House (Philadelphia), Madison Street Club Stable (Wilmington), Henry F. Michell Company (Philadelphia), and Trumans' Pioneer Stud Farm (Illinois).

Other business contacts of William du Pont were predominantly with the companies in which he invested or operated. These contacts appear in Series II: General Correspondence and in Series IV: Business Papers.

William du Pont's role as an associate of Lammot du Pont's in the high explosives enterprises Repauno Chemical Company, Hercules Powder Company and the Torpedo Company is well documented in this collection. Records of the Repauno Chemical Company include extracts from the minute meetings of the board of directors, financial statements, patent specifications, technical and operational materials, agreements between members of the Gunpowder Trade Association on price adjustments and production and sales quotas by regions, and correspondence of William du Pont as the company's secretary, treasurer, and president. His correspondence about companies and the Gunpowder Trade Association financial and organizational issues is complemented by the papers of Repauno's first president Lammot du Pont (1880-1884, about 2 linear ft.). These include business correspondence, notes and memoranda concerned with preparation of agreements, litigation with California Giant Powder Company regarding dynamite patents, negotiations with railroad companies on explosives transportation, and company operations and experiments with dynamite ingredients, especially with sulphuric and nitric acids. This material supplements the collection of the Lammot du Pont Papers at Hagley Library (Accession 384, Papers of Lammot du Pont).

William du Pont became involved in the E.I. du Pont de Nemours Powder Company at the time of its reorganization under the antitrust decree of December 15, 1912. In 1914, he was elected to the board of directors and became chairman of the Financial Committee, but was expelled from both in March 1916 after Pierre S. du Pont took control of the company. William du Pont's papers contain reports, circular letters, financial estimates and forecasts for this short period, and related correspondence.

Another family business which is well documented in the William du Pont Papers is the U.S.F. Powder Company (also known as the U.S. Flashless Powder Company), which was started in 1919 by William du Pont's second cousins, Ernest du Pont (1873-1942) and Francis I. du Pont (1880-1944). William du Pont and, later his son William du Pont Jr., were the company's stockholders and members of the board of directors. The material from their collection represents the company business in its entirety and is probably the most comprehensive source of information on the development and manufacture of flashless powder by the du Ponts. Documents show U.S.F. Powder Company activities from the time when the flashless powder experiments started at the Ball Grain Explosives Company's Granogue plant in early 1918 up to the U.S.F. Powder Company's dissolution in 1945. These records include administrative, financial and technical documents, correspondence, and subject files; numerous patents of Francis I. and Ernest du Pont for their inventions and improvements in the field of smokeless and flashless powder manufacture, with applications and technical specifications; agreements with Atlas Powder Company, E.I. du Pont de Nemours and Company, Nobel Industries, Ltd., and the United States Navy Ordnance Department. Records documenting laboratory experiments with flashless powder samples and results of firing tests performed at Granogue in 1918-1926 are accompanied with glass negatives of the shots of firings, which have been transferred to the Pictorial Collections Department in Accession 2007.205.

William du Pont's role with the Delaware Trust Company--which he bought with Alfred I. du Pont in 1916 and was consecutively vice president (1916-1920), president (1920-1922), and chairman of the board (1923-1928)--is documented in his papers by a small amount of his correspondence with Alfred I. du Pont and company directors. Letters discuss the company's financial statements and reports, banking operations, stockholders issues, employment, and salaries.

The collection contains some papers pertaining to the Montpelier Supply Company, which was organized in 1911 by William du Pont and his associates at his estate in Montpelier, Virginia. The company's business was to buy and sell general merchandise to employees and farmers. Papers contain minute book, store inventories, monthly farm payrolls, du Pont's recapitulations with the company, and lists of local expenses. Correspondence between William du Pont and other members of the board of directors discusses financial and operational matters. The company was reincorporated in Delaware in 1940 by William du Pont Jr., and material pertaining to the later period of company's existence is part of Group 2. Papers of William du Pont Jr.

There are records of the Hinckley Brake Company and Miller Train Control Corporation in William du Pont's papers. Both companies manufactured and sold railroad car brake and stop control devices. William du Pont was a major stockholder and a director of both firms and was one of the organizers and a president of Hinckley Brake Company from 1895. Papers consist of patents for the devices with related correspondence, promotion and reference materials, minute books, and bookkeeping records (Hinckley Brake Company). Additional material for the Miller Train Control Corporation is in the files of Bernard T. Converse (Group 2. Series VII: Business Papers, Sub-series W: Shapdale, Inc., Sub-subseries 4: B.T. Converse Subject Files, folder "Miller Traffic Control").

William du Pont's papers contain material of primarily financial content related to other companies in whose business he was involved, either as a stockholder or a member of the boards of directors: Vacuum Refrigeration Company, United States Refrigeration Company, Virginia Haloid Company, Electro Company, and Brandywine Granite Company.

The files of William du Pont contain numerous enclosures. There are financial statements of many companies (E.I. du Pont de Nemours & 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., National Horse Show Association of America, United Light and Railways Company); prospectuses of banks and investment firms; informational leaflets of the Horse Association of America (more than fifty issues, 1921-1927); of the National Parks Association, 1922-1923; catalogs and advertisements for agricultural products, domestic goods, clothing, and wine; horse and cattle show programs; photographs of horses, dogs, prize items, and buildings of mansions offered for sale; estate auction announcements; blueprints and drawings related to William du Pont's estates; newspaper clippings; restaurant menus; and Christmas cards.

Among individual items, of note are the genealogy of Annie Rogers du Pont on her mother's side (a letter from law offices of Ward, Gray, and Neary, March 10, 1920, shows her remote family connection to the American painter Mary Cassatt); a short history of the American-Russian enterprise Lied Incorporated, organized by Jonas Lied in 1918; and an outline of William du Pont's presentation at a horse show: "Scenario. Thirty Years of Hackney Breeding. By William du Pont" (in Miscellaneous Enclosures).

The William du Pont Papers provide an invaluable source of information about the life and times of an enterprising and successful member of the du Pont family. The papers document his business activities as a participant in the du Pont family enterprises, as a prominent banker and financier, and as an entrepreneur in the American horse industry. His papers contain unique material on one of the lesser-known du Pont family-related explosives enterprises, U.S.F. Powder Company. The collection also provides much information for those interested in the local history of New Castle County, Delaware (Bellevue Hall), Hanover County, Virginia (Montpelier estate) and Glynn County, Georgia (Altama estate).