Born William Erksine Strange in Denver, Colorado, Preston was reared in Laramie in southern Wyoming by his educator parents, John and Bernice Strange. He had two younger sisters, Joan and Mary. In 1947 he graduated from Laramie High School, where he was active in football, track, the school band and the Reserve Officer Training Corps. He attended the University of Wyoming in Laramie, where he studied pharmacy. He became an accomplished musician and played in many bands during the late 1940s. In 1950 Preston was drafted into the United States Army. Trained in an artillery unit at Fort Bliss, Texas, Preston attained the rank of first lieutenant and fought in the Korean War. For a time, after his military Service, he was a park ranger at Grand Teton National Park in northwestern Wyoming and rode the rodeo circuit before he got his break as an actor.