Gary Dilley attended Michigan State University. After the 1964 Olympics, he won four individual NCAA titles in the 100 and 200 yard backstrokes in 1965 and 1966. Dilley also won six Big 10 titles, in both backstrokes in 1965-66 and with the 4x100 freestyle relay team in 1965 and 1967. He also won gold medals at the 1965 Universiade: in the 200 meter backstroke and4 x 100 freestyle relay. Dilley later attended dental school at Indiana University, and then studied orthodontics at the University of North Carolina. He had a dental practice in Cary, North Carolina, specializing in pediatric dentistry and orthodontics until his retirement.