In the U.S., before 1906, people could go to any courthouse to become a citizen. Apparently you could start the process in one court and finish it in another. Papers filed after 27 Sept. 1906 have more info than prior:
- Declaration of Intent/1st papers
- Petition for Naturalization/2nd or final papers
- Certificate of Naturalization. The government didn’t keep copies of this so you may only find them in family papers. If you can’t find copies you can try looking at census records.
The census records of 1870, and 1900-1940 asked if a person was naturalized. In 1920 they asked what year the person was naturalized. Look at the citizenship columns for these abbreviations:
- AL (alien),
- NA (naturalized),
- NR (not reported),
- PA (1st papers filed),
- IN (declaration of intent),
- AmCit (American citizen born abroad was used in the 1940 census).