Can anyone suggest how best to confirm a 1921 out-of-wedlock birth to now-deceased parents as a result of an adulterous domestic cohabitation in the Port Colborne-Humberstone area?

Birth records for 1921 are still protected under the Privacy Act. To access these records either the person whose birth is in question, their legal representative, or someone who can prove they are next-of-kin would have to apply to the Office of the Registrar General. Or wait until 2018 when the 1921 birth registrations will be released for public viewing.

[From Cathy] It is not clear from your question if the baby in question was put up for adoption. If the child was, then it will be a different answer as the name of the child would then be completely different to that of the parents - that child would have the adoptive name instead. If the child was not put up for adoption, then that child would have the mother's surname, not the father's surname. You would search as you would for any person with that surname and date. However, if adoption was involved, I would recommend going to adoption reunion sites instead such as http://www.canadianadopteesregistry.org which has adoptions dating back to the 1920's. It is not comprehensive as only people who voluntarily choose to post the adoptions appear. 1921 is when the Adoption Act of Ontario came into force, so it depends if the adoption (if there was one) occurred before April of that year - it makes a difference as to how to search. It could have been a guardianship if it was before April If you think there could have been a guardianship, then you go to the Ontario Archives (there are no adoption records there). Go to this web page, scroll down to section 8 and following the instructions there on searching.