Foss was born in an unelectrified farmhouse near Sioux Falls, South Dakota, the oldest son of Mary Esther (née Lacey) and Frank Ole Foss. He was of Norwegian and Scottish descent. At age 12, he visited an airfield in Renner to see Charles Lindbergh on tour with his aircraft, the Spirit of St. Louis. Four years later, he and his father paid $1.50 apiece to take their first aircraft ride in a Ford Trimotor at Black Hills Airport with a famed South Dakota aviator, Clyde Ice.