In 1962 he was married to Dorothy Stark Stabler and together they had three children: Giovanna (b. 1963, a diplomat with the Costa Rican government), César (b. 1965, a professor at Illinois Wesleyan University) and Rocío (1967).
Duell graduated from the Green Mountain Junior College (now Green Mountain College) (Vermont), Illinois Wesleyan University, and Yale University.
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The conference was formed with nine charter members (Augustana College, Carthage College, Elmhurst College, Illinois College, Illinois Wesleyan University, Lake Forest College, Millikin University, North Central College and Wheaton College) on April 26, 1946, in Jacksonville, Ill., and opened competition in the 1946-47 academic year as the College Conference of Illinois.
He graduated from Illinois Wesleyan University in 1915, and was a member of Tau Kappa Epsilon.