"Vermont Vital Records, 1760-1954", database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:XFXG-TQK : 19 February 2021), Joseph Willis in entry for Sarah Sophie Willis, 1878.
"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M8YV-G4S : 19 February 2021), Joseph Willis, Monroe, Platte, Nebraska, United States; citing enumeration district ED 96, sheet 217C, NARA microfilm publication T9 (Washington, D.C.: National Archives and Records Administration, n.d.), FHL microfilm 1,254,754.
"Washington Death Certificates, 1907-1960," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:N35V-6VB : 10 March 2018), Joseph Willis in entry for John Willis, 08 Jan 1934; citing Lake Burien, King, Washington, reference cn 22, Bureau of Vital Statistics, Olympia; FHL microfilm 2,023,100.