Dear Mr. Beutler,
Thank you for posting your request on History Hub!
Two copies of the certificate of citizenship were created – one given to the petitioner as proof of citizenship and one forwarded to the Immigration and Naturalization Service (INS). All INS records are now overseen by the US Citizenship and Immigration Services (USCIS). USCIS maintains duplicate copies of court records (including the certificate of citizenship) created September 27, 1906-March 31, 1956 within Certificate Files (C-Files). C-Files can be requested through the USCIS Genealogy Program.
If you are pursuing dual citizenship, the Consulates are aware that USCIS does NOT provide certification of files in their holdings. Instead, you must present the photocopy of the document(s) along with the USCIS Genealogy Program response letter and mailing envelope.
We hope this is helpful. Best of luck with your family research!
Thank you. And thanks to whomever it was who fixed my misspelling of "naturalization."