William was born William Lewis Tomlinson but was raised by Washington Barnum (1849-1931) and Ann Eliza Bale Barnum (1848-1931), adopting the surname Barnum as an adult.
From the Sunfield Sentinel, Sunfield, Eaton County, Michigan, October 18, 1945: Obituary: William L. Barnum, 69, died at his home in Sunfield, October 14. He was born in Sunfield township, January 25, 1876. Mr Barnum had been ill several weeks and had been in the St. Lawrence Hospital part of the time. Surviving besides the wife, Gertrude, are six children, T/Sgt. Otto W. Barnum, stationed at Reno, Nevada, T/Sgt. Oren F. Barnum, serving in the Pacific area, Mrs. Ina Holton, Mrs Iva Weiler, Mrs Alta Williams, and Susie at home, also eight grandchildren, several nieces and nephews. Funeral service were held Wednesday at 2 o'clock at the Mapes funeral home in Sunfield, Rev. M. D. Burtch officiating. Interment in the Sunfield cemetery.
He was buried in Sunfield Cemetery.