Son of Oscar Ludwig Johnson and his first wife, Catherine Dreher. His parents divorced prior to 1917, per his father's WWI draft registration. That draft card stated that Oscar was supporting his 5 year-old son; no mention was made of Clarence's older sister, born in 1911 (apparently died young).
Ohio death records indicate that Clarence was preceded in death by his wife. The 1940 census shows Clarence and Margery M. Johnson residing in Monmouth. The obituaries of his step-father in 1959 and his father in 1979 state that Clarence was residing in Pittsfield, Illinois.