Sound genealogy methodology indicates that witnesses on documents should always be researched for a potential connection to the person for whom they are witnessing a document. That’s good advice. Just remember that not every witness had a connection to the person who actually was signing the document.
Samuel Neill became a citizen in Hancock County, Illinois, in 1880. A quick search of the 1880 census indicated that the witness on his naturalization was the county collector who apparently had no connection to Neill other than he was in the courthouse on the day Neill naturalized. Sometimes witnesses are simply other adults of legal age who were in the vicinity of your ancestor.