Hagerthy, the son of Ford Hagerthy (1907–1996) and Rita Hagerthy (1911–1998), is a South Dakota native. He was living in Los Angeles, California by the late 1930s. He and his wife, Judith A. Hagerthy (born ca. 1940), reside in Corona del Mar, a neighborhood in Newport Beach, California. The couple has two children, Kelly Ann Hagerthy (born ca. 1961) and Patrick R. Hagerthy (born ca. 1963). After his acting career ended, Hagerthy entered the real estate Business in southern California.