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Naturalization records dated prior to October 1991 from the Federal courts are at the National Archives. To determine which NARA field site maintains Federal court records for the state where you or your relative was naturalized, please visit: https://www.archives.gov/research/court-records. You will need to work directly with staff in that office in order to obtain a copy of the requested record.
In most cases, the National Archives will not have a copy of the certificate of citizenship granted to a petitioner – our holdings normally include only the declaration of intention (with any accompanying certificate of arrival) and petition for naturalization.
Naturalization records from state or local courts are often at state archives or county historical societies.
Researchers may need to contact USCIS or the Federal court in order to obtain copies of certain post-1906 naturalization records.
If the naturalization took place in a Federal court, the declaration of intention (with accompanying certificate of arrival) and petition for naturalization will usually be in the National Archives facility serving the state in which the Federal court is located (https://www.archives.gov/research/court-records).
Normally, the National Archives will not have a copy of the certificate of citizenship. If the naturalization occurred September 27, 1906 - March 31, 1956, the certificate should appear within a Certificate File (C-File) that can be obtained through the US Citizenship and Immigration Services (USCIS) Genealogy Program.
We hope this information is helpful in your research.
The National Archives and Records Administration