This doesn't help with the marriage, but John is living with his family in Evanston, Illinois in 1920 but not in 1930.
"United States Census, 1920", database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:MJWQ-1Z7 : 1 February 2021), John Ferguson in entry for Anthony Ferguson, 1920.
"United States Census, 1930," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:XSRM-2KZ : accessed 7 March 2021), Anthony Ferguson, Evanston, Cook, Illinois, United States; citing enumeration district (ED) ED 2131, sheet 11A, line 32, family 126, NARA microfilm publication T626 (Washington D.C.: National Archives and Records Administration, 2002), roll 500; FHL microfilm 2,340,235.