The N-400 (Application for Naturalization) can be filed online or by mail. Where you send a paper N-400 depends on your current state of residence and, in some cases, which USCIS service center is handling your application type. This guide covers both options — online filing (which is straightforward) and paper filing (which requires finding the correct mailing address).
Before you file, be aware that USCIS mailing addresses change periodically. Always verify the current filing address at uscis.gov before mailing your application — this guide reflects general filing patterns as of 2026, but the definitive source is always the official USCIS website.
Most N-400 applicants can file online through the USCIS website at uscis.gov/n-400. Online filing has several advantages:
Online filing is available for most standard N-400 applicants — U.S. permanent residents applying based on 5 years of residence, spouses of U.S. citizens applying based on 3 years of residence, and members of the military.
Some applicants still need to file by paper: those with complex case histories, certain exceptions, or situations where USCIS requires original documents that can't be uploaded. If you're unsure, an immigration attorney can help you determine the appropriate method.
If you're filing by paper, USCIS routes N-400 applications to different lockbox facilities and service centers based on your state. Here's the general routing structure (always verify at uscis.gov before mailing):
Serves applicants from most western and central states, including Arizona, California, Colorado, Nevada, New Mexico, Oregon, Utah, Washington, and others. The specific P.O. Box addresses differ for regular mail vs. USPS Express Mail vs. FedEx/UPS — check uscis.gov for the exact addresses by carrier type.
Serves applicants from Midwest and some central states, including Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota, Wisconsin, and others.
Serves applicants from southern and southeastern states, including Texas, Louisiana, Mississippi, Alabama, Arkansas, Oklahoma, and others.
Some N-400 applicants from certain states may use the Elgin, Illinois facility. Check uscis.gov for current routing by state — the exact state-to-lockbox assignments do change.
Serves applicants from the remaining southeastern states and the eastern seaboard in some configurations, including Florida, Georgia, North Carolina, South Carolina, and others.
Important: The mailing address and state-to-facility routing can change when USCIS adjusts its operational capacity between service centers. The routing that was correct in 2024 may not be the same in 2026. Always go to the direct USCIS N-400 page to confirm before mailing.
Filing by mail requires more than just the completed form. You'll need to include:
Do not send original documents unless USCIS specifically instructs you to. Originals can get lost in processing; certified copies are what USCIS actually needs at this stage.
The standard N-400 filing fee as of 2026 is $760 for paper filing ($760 for online filing as well — both methods pay the same combined form + biometrics fee). This includes the $85 biometrics service fee for fingerprinting and background checks.
Fee waiver (Form I-912) is available for applicants who demonstrate financial hardship or receive means-tested benefits. You submit the fee waiver request with your N-400 at the same time — USCIS decides on the waiver before processing your application.
Military applicants (current and certain veterans) file for free — there's no fee for naturalizing members of the armed forces.
Once USCIS receives your application, here's what happens:
Current N-400 processing times vary significantly by field office and application volume. Historically, processing runs 12–24 months for most applicants, though some offices process faster and some have backlogs extending beyond that range.
You can check current processing times for your specific field office at uscis.gov/tools/reports-and-studies/immigration-forms-data. Enter Form N-400 and select your local field office to see estimated times.
If your case is significantly outside the normal processing time for your office, you may be able to file a case inquiry or, in some situations, a mandamus lawsuit — but that's typically reserved for cases well beyond the office's stated processing window.
Filing the application is just step one. The civics test at the interview is where many applicants feel unprepared. The 100 civics questions are publicly available on the USCIS website — you can start studying them the moment you file your application. The 10 questions you'll be asked at your interview will come from that list, and you need to answer 6 correctly to pass.
Common areas where applicants struggle: U.S. history questions (especially dates and names), the full structure of the federal government, and specific constitutional rights. Our practice tests cover the civics content and the procedural aspects of the N-400 process — from eligibility and supporting documents to common pitfalls that lead to delays or denials.
Filing your N-400 is a significant step, but it's the beginning of a process that typically takes over a year. Use that time wisely. Study the civics questions starting now — don't wait until you receive your interview notice. By the time your interview date arrives, the 100 questions should feel easy.
Our N-400 practice tests cover civics preparation, eligibility requirements, required supporting documents, processing time expectations, and common application pitfalls — the areas where applicants most often make mistakes that delay or complicate their naturalization. Work through them to understand the full process, not just the filing step.
The path to U.S. citizenship is one of the most significant legal processes a person can undertake. Filing the paperwork correctly, understanding what comes next, and walking into your interview fully prepared are all things within your control. Start with what you can control today.