Series 6: Subject Files, includes correspondence, reference materials, newsclippings, meeting minutes, agendas, and other materials documenting those aspects of Stevenson's professional life not addressed in other series, including his governorship of Illinois, service on the boards of trustees for various companies and philanthropic organizations, his law career, government service during the New Deal and World War II, and political activities outside his presidential campaigns.

Stevenson served on the boards of trustees for a number of organizations, including the Eleanor Roosevelt Foundation, Encyclopedia Britannica, Hull House, Daily Pantagraph, and the Field Foundation. Papers documenting Stevenson's organizational affiliations, such as the Chicago Council on Foreign Relations, Chicago Bar Association, and the Committee to Defend America by Aiding the Allies, are also included. Clearly illustrated throughout this series is Stevenson's high level of involvement with a variety of organizations, ranging from social service to political groups. Stevenson's devotion to Chicago's institutions, well after he became a nationally – and internationally – prominent figure, is shown.

Stevenson's memoranda to president-elect John F. Kennedy, advising him on his first important actions as President (most notably appointing a Secretary of State) are particularly interesting.