After returning to the U.S. to complete his graduate studies, he received a Ph.D. from the University of Chicago in 1940.
Rockefeller ensured that selected members of the fourth generation, known generically as the cousins, became directly involved in the family's institutions. This involved inviting them to be more active in the Rockefeller Brothers Fund, the principal foundation established in 1940 by the five brothers and their one sister. The extended family also became involved in their own philanthropic organization, formed in 1967 and primarily established by third-generation members, called the Rockefeller Family Fund.
In 1940, Rockefeller married Margaret "Peggy" McGrath, who died in 1996. They had six children:
The Kykuit section of the Rockefeller family compound is the location of The Pocantico Conference Center of the Rockefeller Brothers Fund – established by David and his four brothers in 1940 – which was created when the Fund leased the area from the National Trust for Historic Preservation in 1991.