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To determine if your ancestors ever applied for naturalization, you will want to request a search of their records from the appropriate National Archives location. 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.
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.
We hope this information is helpful in your research.
The National Archives and Records Administration