"United States Census, 1920," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MJCS-8V8 : accessed 29 January 2020), Oliver Whitfoht in household of John Whitfoht, Limestone, Peoria, Illinois, United States; citing ED 58, sheet 22A, line 33, family 477, NARA microfilm publication T625 (Washington D.C.: National Archives and Records Administration, 1992), roll 398; FHL microfilm 1,820,398.
"United States Census, 1940," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:KWZT-X63 : 16 November 2019), Oliver Wittfoht in household of John Wittfoht, Fondulac Township, Tazewell, Illinois, United States; citing enumeration district (ED) 90-15, sheet 3B, line 44, family 56, Sixteenth Census of the United States, 1940, NARA digital publication T627. Records of the Bureau of the Census, 1790 - 2007, RG 29. Washington, D.C.: National Archives and Records Administration, 2012, roll 894.
"United States Social Security Death Index," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:V9WH-T6P : 19 May 2014), Oliver W Wittfoht, 09 Mar 1992; citing U.S. Social Security Administration, Death Master File, database (Alexandria, Virginia: National Technical Information Service, ongoing).