The Delaware Land Development Company was incorporated by William du Pont Sr. on March 25, 1926, when he transferred to it his property called Westover Hills, situated to the west of the Wilmington Country Club, "for development into high-class restricted home sites, with all modern improvements" (letter from the president of Delaware Land Development Company to Mr. F. B. Davis Jr., August 6, 1926). John W. McComb was the company's first president until his resignation in September 1944, upon which William du Pont, Jr. assumed the presidency and held it until his death on December 31, 1965.

The development of Westover Hills was undertaken in several stages and developed sections were named A, A extension, B, C, D, and E. Documents in the collection refer to the related section, the block inside the section, and the lot numbers in the block. To maintain the property of the developed and sold sections, service companies were organized: Maintenance Corporation of Westover Hills for section A and A extension in March 1928; Service Corporation of Westover Hills for section C in April 1932; and Westover Hills-Woods, Inc., for section E in January 1969, when the Delaware Land Development Company had already dissolved, but was still empowered to transfer rights to the maintenance company.

The Westover Hills project remained the company's core business until its dissolution on December 30, 1966, but from 1945, Delaware Land Development Company activity was confined to the sales of previously developed parts of Westover Hills, while undeveloped lots were sold to the newly organized Westover Hill, Inc., which served as an agent for du Pont's sister Marion du Pont Scott.

Among the du Pont family members who bought properties at Westover Hills were William du Pont, Jr.'s eldest daughter Jean Ellen du Pont McConnell and her second husband J. H. Tyler McConnell, who obtained two lots in March 1959.

Besides the Westover Hills development, the Delaware Land Development Company in 1926-1930 was involved in the acquisition of land situated in Cecil County, Maryland, which was later transferred to its subsidiary Stockford Farms, Inc., and used for agricultural projects. Another activity of Delaware Land Development Company started in February 1929 with the erection of a two-wing addition to the Delaware Trust Building, which later that year was assumed by the newly organized Delaware Trust Building Corporation.

The company's management had intended to re-incorporate the company under the name of Delaware Land Development Corporation and filed for incorporation with the Secretary of State on August 16, 1935. The accompanying letter of August 15, 1935, states: "The persons interested in this Company...desire to take out a new charter in the name of Delaware Land Development Corporation. Please be advised that this Company consents to the issuance of a charter in said name. The new Company will carry on the business of the present company and it is the intension to dissolve the present company as soon as it can conveniently be done." Nevertheless, the company acted under the name of Delaware Land Development Company until its dissolution in 1966. Eighty numbered and five unnumbered bonds of the Delaware Land Development Corporation were issued at that time, but they were kept unassigned with the papers of the Delaware Land Development Company.