Johnson lives with his wife, Shirley, along Mercer County Highway 31 near the Oliver County border. The couple have two daughters and two grandchildren. Johnson is a member of the American Legion, Veterans of Foreign Wars, Vietnam Veterans of America and Eagles Club. Johnson was assistant Mercer County States Attorney for eight years, practiced law in Garrison, and served as Sioux County States Attorney for four years. He was elected to his first term as states attorney for Mercer County in 1999.