Cooper graduated from Central High School in 1940 and attended Ohio State University in 1941. He then served in the United States Coast Guard from 1942 to 1946."Harold M. Cooper",legacy.com, Retrieved on September 2, 2017 After the war, he took a position in Columbus with the National Association of Professional Baseball Leagues (later known as Minor League Baseball) before heading to Hutchinson, Kansas, where he would be named The Sporting News Minor League Executive of the Year in 1950 while running the Western Association affiliate of the Pittsburgh Pirates.
