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If you were naturalized after February 27, 2001, and you were a permanent resident and under 18 years old at the time, then you probably have automatically acquired U.S. citizenship. Before that date, you may have automatically acquired U.S. citizenship if you were a permanent resident and under 18 years old when your mother was naturalized, or if you had only one parent when that parent naturalized. However, if your parent(s) naturalized after you were 18, then you will need to apply for naturalization on your own after you have been a permanent resident for at least 5 years.
You can apply to the U.S. Department of State for a U.S. passport. A passport will be evidence of citizenship and also serves as a travel document if you need to travel.
If you need copies a copy of your mothers naturalization documents there are several ways to get copies for your proof of citizenship. If your mother is alive, she can apply for new certificates or submit Freedom of Information Act requests for proof of when they naturalized. If she has passed away, you can order a copy of her naturalization certificates online from the U.S. Citizenship and Immigration Services. Just go to uscis.gov and click on “History and Genealogy” on the left side of the page. Another source for proof of her naturalization is the New York Office of the National Archives, Alexander Hamilton U.S. Custom House at One Bowling Green, Manhattan, or online at www.archives.gov/northeast/nyc/. The National Archives in New York City is the repository for naturalization records filed in federal courts in New Jersey, New York and Puerto Rico from 1795 to 1991.
I hope this helps.