Cooper was the father of Maciej Słomczyński. Słomczyński was a Polish translator and writer. He took his step-father's name when his mother married. Cooper married film actress Dorothy Jordan on May 27, 1933. They kept their marriage a secret from Hollywood. A month later, journalists reported it. Cooper had a heart attack later that year. In the 1950s he supported Joseph McCarthy in his mission to root out Communists in Hollywood and Washington, D.C.