Cornelius J. Gleeson was born on December 14, 1926 in Middletown, Connecticut, U.S.A. In 1945, he was drafted out of Woodrow Wilson High School, Middletown, Connecticut, at the end of his Junior year and served in the Army Air Force, Financial Department, Military Police and as a P.O.W. Guard.
On Thanksgiving Day 1946, he returned home and graduated from high school in the spring of 1947.
Gleeson studied mehanical drawing and architecture and then entered the family home-building business with his brother. A short time later, his father passed away after spending several days in the hospital.
Around this time, he entered the Secret Service. No one knew this, except for his mother.