Certificate Files, September 27, 1906 - March 31, 1956

What are C-Files?

Certificate Files, or "C-Files,"  document naturalizations - the acquisition of United States citizenship after birth. C-Files contain copies of records evidencing the:

  1. Granting of naturalized U.S. citizenship by courts between from 1906 to 1956; and
  2. Issuance of Certificates of Citizenship to those who derived or resumed U.S. citizenship.

C-Files are a product of the Basic Naturalization Act of 1906. That law created the Federal Naturalization Service and required the new agency to collect and maintain copies of all naturalization records nationwide. The C-File series later expanded to include records of U.S. citizenship acquired by derivation (naturalization by virtue of qualifying relation to another who is a birthright or naturalized citizen) and resumption or repatriation by former citizens that expatriated themselves (lost their U.S. citizenship).

Between September 27, 1906 until March 31, 1956, the Federal Naturalization Service stored its citizenship records in C-Files. Certain C-File documents are duplicated in the records of naturalization courts across the nation. Other C-File documents are unique.


 The United States adopted judicial naturalization in 1790 and the nation's courts conducted most naturalization proceedings until the late 20th century. For most of American history, an immigrant seeking naturalization almost always petitioned a court. A judge decided the applicant's eligibility for citizenship and entered an order either granting or denying the petition. The clerk of the court then made a permanent record of the proceedings in the court's records.

Before the Basic Naturalization Act of 1906, the United States lacked a central repository for naturalization records. Each naturalization court could issue its own version of naturalization certificate and only the naturalization court itself retained a copy of an immigrant's naturalization records.

The Basic Naturalization Act of 1906 required naturalization courts to begin using standard naturalization forms for the first time and the new Federal Naturalization Bureau to keep duplicate copies of all court naturalization records beginning on September 27, 1906. Thereafter, courts forwarded copies of Declarations of Intention, Petitions for Naturalization, and Certificates of Naturalization to Washington, D.C. The Naturalization Service filed the copies of court naturalization records from across the country in its C-Files.

Subsequent naturalization acts expanded the Naturalization Service’s authority and allowed the creation of additional C-Files relating to derivative citizenship, resumed U.S. citizenship, and repatriation. The Bureau of Naturalization’s various programs ultimately resulted in ten unique sub-series of C- Files. Each of the ten C-Files sub-series is distinguished by the method of obtaining U.S. citizenship or the legislation under which an immigrant’s citizenship was granted:

Naturalized Citizens – Persons granted U.S. citizenship after birth upon their own application:

  • C-Files – Naturalization Certificate Files;
  • OL C-Files – Old Law (pre-1906) Replacement Certificate;
  • OM C-Files – World War II Overseas Military Naturalizations; and
  • OS C-Files – Overseas Military Naturalizations during and after the Korean War.

Derivative Citizens – Persons automatically acquiring U.S. citizenship by virtue of their relationship to an American citizen:

  • Derivative A C-Files – Derived through the naturalization of parent or spouse; and
  • Derivative AA C-Files – Derived through birth abroad to a U.S. citizen parent.

Repatriated Citizens – Persons readmitted to U.S. citizenship after relinquishing their citizenship by some voluntary action:

  • B Certificates – Repatriations prior to January 13, 1941;
  • D Certificates – Repatriations after January 13, 1941;
  • 3904/Series Records – Applications to resume citizenship; and
  • 129/Series Records – Repatriation of women who lost U.S. citizenship by marriage to an alien prior to passing of the Cable Act ("Married Women's Citizenship Act") in 1922.

For more information about the 10 C-Files Series, see the Certificate Series table.

The C-Files Today 

USCIS is the current custodian of the C-Files. USCIS' predecessor, the Immigration and Naturalization Service (INS), microfilmed C-Files dated 1906 to ca. 1944 (C-1 to C-6500000) in the 1950’s. Sadly, the original files were destroyed. The only C-files below C-6499999 remaining in paper form are those that were:

  • Unavailable at the time of filming; or
  • Re-opened after microfilming for further action.

Immigrants with C-Files below C-6500000 may have additional USCIS files depending on their arrival date or naturalization date. Some C-Files below C-6500000 are “Consolidated C-Files.” Consolidated C-Files are the only file on an individual subject and contain all agency records pertaining to that immigrant. Consolidated C-Files are only available in hard copy. 

C-Files numbered C-6500000 to approximately C-7700000 (up to March 31, 1956 when the file series closed) are all “Consolidated C-Files” and available only in paper form.

The Research Value of C-Files 

C-Files contain copies of records relating to all:

  • U.S. naturalizations in Federal, State, county, or municipal courts between September 27, 1906 and March 31, 1956;
  • Overseas military naturalizations during that half century;
  • Replacements of "old law" naturalization certificates (certificates issued before 1906);
  • Issuances of Certificates of Citizenship in derivative citizenship; and
  • Repatriation and resumption of citizenship cases.

Biographical Content of Forms –The standardized naturalization forms introduced by the Federal Naturalization Act in 1906 called for the immigrant’s name, date and place of birth, and port and date of arrival. Declarations of Intention and Naturalization Certificates issued after July 1, 1929, also include a picture of the petitioner.

Reliability – Confirmation of naturalization applicants' information by the courts and Naturalization Service Examiners made C-Files reliable records. When applicants claimed arrival after June 30, 1906, the Naturalization Service verified the arrival information by checking the original immigration arrival record. For more information about immigration arrival records, which are now preserved by the National Archives and Records Administration (NARA), see NARA's immigration research page.

Naturalization Records Duplicated in Court Records – Original records of judicial naturalization are court records, including Declarations of Intention and Petitions for Naturalization. Some courts also retained Certificates of Arrival (evidencing lawful admission to permanent residence) issued by the Immigration Service among their records.

Between September 27, 1906, and the early 1990’s, naturalization courts maintained original judicial naturalization documents and sent duplicate copies to Washington D.C. to be filed with the U.S. Naturalization Service. Accordingly, most but not all, naturalization records can be found among court records.

Naturalization Records Not Duplicated in Court Records – Despite the standardization mandated by the 1906 naturalization law, different C-Files may contain different forms and not all C-File documents will be duplicated in court records (i.e., these records are only available from USCIS). When an immigrant naturalized, the provisions of law under which s/he applied for citizenship, and whether there was any further activity in his or her case after naturalization could all affect the records contained in his or her C-File. The different types of naturalization records in an immigrant’s C-File may provide valuable clues into the events of his or her life:

  • Reopened Cases – Many naturalization cases re-opened later in connection with applications for replacement (of lost) certificates, derivative citizenship claims, requests for proof of citizenship in relation to job applications, background investigations, insurance claims, or pension benefits. In such cases, additional information not appearing in the original court records may have been added to re-opened C-files.
  • Record Types Unique to C-Files – USCIS C-Files also include several certificate sub-series not duplicated in court records. These unique records relate to:
    • Additional applications, correspondence, and documents relating to a specific judicial naturalization;
    • Applications for certificates of derivative citizenship (by wives and children of U.S. citizens);
    • Applications for replacement certificates of citizenship or certificates of naturalization;
    • Oaths of repatriation administered at U.S. Consulates and Embassies abroad;
    • Documents related to expatriation; and
    • Administrative naturalization files of members of the U.S. Armed Forces naturalized overseas and not documented in any domestic court.

Avoiding Common Index and Records Request Issues With C-Files

Careful attention to the information contained in your Index Search and Record Requests could save you time and money. Please be mindful of the following:


Index Search Issues – The most frequent complication encountered when searching for C-Files is identifying the correct naturalized citizen when many other immigrants have the same or similar names and dates of birth. If multiple index references match the requested immigrant, reference to the actual records can help locate the right file. Whenever available, please include the following biographical information with your Index Search Request. Any of these facts could distinguish your immigrant:

  • Arrival information – Date and port of entry (or an estimate);
  • Names of spouse and/or children – Family members’ names usually appear in naturalization records, because children and wives often automatically derived citizenship from the naturalization of a parent or husband (Married women acquired the citizenship of their husband under U.S. law until the passage of the Married Women’s Citizenship Act of 1922);
  • Occupation;
  • Place of birth – Country and region, city, or town if available; and
  • Place of residence when naturalized – All places where the immigrant lived (or may have lived), with street addresses if possible.

Record Request Issues – Unless you are certain of your immigrant's C-File number, you are strongly encouraged to submit an Index Search Request before your Records Request. Besides avoiding a wrong number, the Index Search may also identify additional immigration records that you may want to include in your Records Request.

  • Wrong Numbers – The Genealogy Program often experiences problems when researchers submit Record Requests containing the wrong C-number.  Some researchers confuse the naturalization court’s petition number with a C-number. Others misunderstand annotations found on ship passenger lists or other documents and think they are C-numbers (or A-Numbers). If the number provided in a Records Requests relates to a file where the name is not the same name provided in the request, no file will be returned and there is no refund.
  • Image Quality – Some C-File microfilm was poorly produced a half-century ago and has deteriorated since. Record images may be faded, but our staff work to provide the best possible record copy.
  • Privacy Restrictions – C-Files may include documents containing personal information about other persons (called "third parties") who may still be living. This occurs in C-Files if/when the petition lists the minor children of the immigrant. A document containing third party personal information is not releasable outside the Freedom of Information (FOIA) process, so some records received from the Genealogy Program could have some information redacted.

For more information about where to find C-File Numbers, see Where to Find a C-File Number.

C-Files Image Gallery

The images shown in this gallery are of typical documents found in C-Files and are for representative purposes only. Some data have been omitted due to privacy reasons. Documents availability vary by case.


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