You have a very large amount of information about this person, but don't know his surname?
Is the information you have from a document of some sort? If so, I would suggest going back to this document to see if there are any further clues.
If that fails you might look in some of the available document collections for people named Spencer who were born in Illinois around 1919 and try to identify possible Norwegian surnames. You could try searching in the US census for 1920 and 1930. And you could try searching the Cook County birth certificates for 1878-1922 (https://familysearch.org/search/collection/show#uri=http://h...
) in case he was born in Cook County.
I did see a Spencer C Peterson, likely birth year 1919, with parents Andrew (born Illinois, but both parents born Norway) and Anna (born Norway). In the 1920 census this family is in Dayton Township, La Salle County, with an older brother Ambrose. In the 1930 census this family is in Mission, La Salle County, with older brother Ambrose and younger sister Annetta (but Annetta is only 3 years younger than Spencer).
I don't know what else to suggest.