Hagel was born in North Platte, Nebraska, a son of Charles Dean Hagel, and his wife Elizabeth (Betty) Dunn. His father was of German heritage, while his mother was of Irish and Polish ancestry. Growing up, Hagel lived across Nebraska; in Ainsworth, Rushville, Scottsbluff, Terrytown, York and Columbus. Hagel was the oldest of four brothers. His father, a veteran of World War II, died suddenly on Christmas morning, 1962, at the age of 39, when Hagel was 16. He graduated from St. Bonaventure High School (now Scotus Central Catholic High School) in Columbus, Nebraska, in 1964, the Brown Institute for Radio and Television in 1966, and he earned a BA degree in history at the University of Nebraska at Omaha in 1971.