This may be off-list, but thought it helpful for searching for Ontario ancestors. It is from another list and I have no additional knowledge. "Often enough, the numbers listed on a census record by a person's name were U.S. Immigration Manifest Annotations. These numbers indicated that an individual had traveled outside the country and was given a re-entry permit, or they could indicate the date and place where an immigrant applied for naturalization. I refer you to the excellent article and web page by Marian L. Smith, a former employee of the U.S. Immigration and Naturalization Service. http://www.jewishgen.org/infofiles/manifests/ " Marjorie