Hefner's mother was of Swedish descent, and his father had German and English ancestry.
Hefner was born on April 9, 1939 in Chicago, Illinois. He was the first child of Grace Caroline (née Swanson; 1895-1997), a teacher, and Glenn Lucius Hefner (1896-1976), an accountant. His parents were from Nebraska. He had a younger brother, Keith (1929-2016).