N-400 Mailing Address USCIS Lockbox — Filing Guide

Where to Mail Your N-400 Application

UCSIS operates multiple lockbox facilities that receive and process Form N-400 applications for naturalization. The correct mailing address depends on two variables: the state you live in, and whether you are filing with standard processing or requesting military naturalization based on service. Sending your application to the wrong facility will not forward it — USCIS returns misfiled packets, and you lose weeks rebuilding the submission with correct fees and signatures.

As of January 2026, USCIS assigns Form N-400 to lockbox facilities in Phoenix, Arizona and Lewisville, Texas. Your state determines which one receives your packet. The lockbox address is not the same as your local field office address — field offices do not accept mailed applications. You will visit a field office later for your interview and oath ceremony, but the application itself must go to the lockbox that serves your region.

USCIS Lockbox Addresses by State

The table below lists the correct N-400 mailing address based on your current residential state. If you are filing from a U.S. territory or a foreign country under certain circumstances, the instructions on the current Form N-400 page at uscis.gov/n-400 specify the address — verify it before mailing.

Military naturalization applicants filing under INA 328 or 329 use a separate address regardless of state: USCIS, P.O. Box 4380, Chicago, IL 60680-4380 for USPS, or USCIS, Attn: N-400 Military, 131 S. Dearborn Street, 3rd Floor, Chicago, IL 60603-5517 for courier services. Confirm this address on the current N-400 instructions before mailing — military naturalization procedures occasionally receive updated routing.

Here's the Honest Answer: Mailing to the Wrong Lockbox Means Rejection

USCIS does not forward misrouted applications to the correct facility. If you send your N-400 packet to the Phoenix lockbox when your state is assigned to the Lewisville lockbox, the Phoenix facility returns the entire submission — application, fee, photographs, and supporting documents — without processing it. Your filing date is lost. When you re-submit to the correct address, you start over with a new receipt date, which affects how soon your priority date is reached and your interview scheduled.

The error costs more than time. Personal checks and money orders have expiration windows; if your packet is in transit and then returned, the payment instrument may no longer be valid by the time you re-file. USCIS requires current fees — as of 2026, confirm the N-400 filing fee on the official USCIS fee schedule at uscis.gov/forms before you mail anything. Fee amounts change periodically via Federal Register notice, so verify the current figure rather than relying on older references.

The Difference Between USPS and Commercial Courier Addresses

Lockbox facilities maintain two separate receiving points: a P.O. Box for U.S. Postal Service standard mail, and a street address for commercial couriers such as FedEx, UPS, and DHL. You cannot send a courier package to the P.O. Box address — courier services do not deliver to post office boxes. Similarly, you cannot send standard USPS mail to the street address and expect it to arrive; that address is a courier-only receiving dock.

Choose one method and use the corresponding address from the table above. Most applicants use USPS standard mail because it is less expensive and the lockbox P.O. Box address is the default routing. If you want delivery confirmation, tracking, and a guaranteed timeline, use a commercial courier with the street address. Either method works — the requirement is matching the service to the correct lockbox address for that service.

What If I Recently Moved to a Different State?

Your filing address is based on your current residential state at the time you sign and mail Form N-400. If you moved from a state assigned to one lockbox to a state assigned to another lockbox after you prepared your application but before you mailed it, update the mailing address on the envelope to match your new state's lockbox assignment. USCIS will schedule your interview and oath ceremony based on the residential address you list in Part 3 of the form, not the lockbox you mail to, so the two do not need to align geographically — the lockbox is only the intake facility.

If you move after USCIS receives your N-400 but before your interview, file Form AR-11 to report the address change within 10 days, then submit a separate change-of-address request specific to your N-400 case using the USCIS Contact Center or your online account. Your interview will be rescheduled to a field office near your new address if the move crosses field office jurisdictions.

What If I Am Filing From Outside the United States?

U.S. citizens living abroad who are eligible to apply for naturalization under INA 319(b) or INA 316(b) must file Form N-400 according to the instructions for overseas applicants. As of 2026, those instructions direct certain applicants to mail the form to a domestic lockbox address and others to file electronically or through a consular post, depending on eligibility category. The most current version of the N-400 instructions at uscis.gov/n-400 specifies the procedure — do not assume the domestic lockbox table above applies to foreign filings without verifying the overseas-applicant section of the official instructions first.

What If I Am Filing Based on Military Service?

Applicants seeking naturalization under INA 328 (service during peacetime) or INA 329 (service during periods of hostility) use a dedicated military lockbox address in Chicago, Illinois, listed in the table above. This address is the same regardless of your residential state or military duty station. Military naturalization applicants do not pay the standard N-400 filing fee — verify the current fee waiver requirements in the N-400 instructions for military members before submitting your packet. If you are filing based on marriage to a U.S. citizen who is in military service but you yourself are not a service member, you use the standard lockbox address for your state, not the military address.

Preparing Your N-400 Packet for Mailing

The lockbox receives thousands of applications daily. Packets that arrive incomplete, incorrectly addressed, or with the wrong fee are rejected and returned. Before you mail:

1. Sign and date the form. An unsigned N-400 is automatically rejected. The signature date should be the date you actually sign it, not a future date or the date you plan to mail it.

2. Include the correct filing fee. As of 2026, verify the current N-400 fee at uscis.gov/forms. Payment must be by personal check, money order, or cashier's check made payable to "U.S. Department of Homeland Security." Do not abbreviate the payee name. Write your full name and "N-400 Application" on the memo line. USCIS does not accept cash.

3. Attach two passport-style photographs that meet USCIS photo specifications. Write your name and Alien Registration Number (A-Number) lightly in pencil on the back of each photo.

4. Include a photocopy of your Permanent Resident Card (front and back on one page). If your card has been lost or stolen, include a copy of your most recent filing receipt or approval notice showing your A-Number.

5. Organize supporting documents in the order listed in the N-400 instructions. Use paper clips, not staples, to attach documents to the form. Do not bind or hole-punch the packet.

6. Mail the packet in a large envelope that accommodates the documents flat without folding. Folding the form can damage the barcode USCIS uses for intake scanning.

Keep a complete copy of everything you mail — the signed form, all supporting documents, the check image, and proof of mailing. If the packet is lost or the lockbox requests additional evidence, you will need your file copy to respond.

Tracking Your N-400 After Mailing

If you mail via USPS Certified Mail with Return Receipt or via a commercial courier with tracking, you will receive confirmation when the lockbox receives the packet. That delivery date is not your filing date. USCIS assigns a filing date (also called the receipt date) after the lockbox opens the envelope, logs the payment, and enters the case into the system. You will receive a Form I-797C Notice of Action by mail within 2 to 4 weeks of USCIS receiving your packet. The receipt notice lists your case number, filing date, and the biometrics appointment scheduling window.

If you do not receive a receipt notice within 30 days of confirmed delivery, contact the USCIS Contact Center at 800-375-5283. Have your tracking number and proof of mailing ready. Do not re-file without confirming that the first packet was actually lost — duplicate filings create case conflicts that delay both applications.

You can check case status online at egov.uscis.gov/casestatus once you have the receipt number from your I-797C notice. Status updates typically occur after the biometrics appointment, after the interview, and when the oath ceremony is scheduled.

Common Mailing Mistakes That Cause Rejection

The Law Offices of Peter D. Chu in San Diego sees recurring errors in returned N-400 packets:

• Wrong lockbox — applicant used the address for a different state or an outdated address from an old instruction sheet
• P.O. Box used with courier or street address used with USPS — mismatched service and address type
• Unsigned form — the most frequent single rejection reason
• Incorrect fee — applicant paid the old fee amount after a fee increase or rounded the fee instead of paying the exact amount
• Payment made to the wrong payee — "USCIS" instead of "U.S. Department of Homeland Security"
• Missing required documents — no Permanent Resident Card copy, no photographs, or photographs that do not meet USCIS specifications

Every rejection delays the naturalization timeline by the time it takes for USCIS to return the packet, for you to identify and fix the issue, and for you to re-mail the corrected application. The corrected packet starts over with a new filing date — it does not retain the original date.

When to Consult an Immigration Attorney

Form N-400 itself is straightforward for applicants with continuous residence, no criminal history, and no time outside the United States beyond brief trips. The complexity arises when your situation does not fit the default path — interrupted residence, prior removal proceedings, certain criminal convictions, tax compliance questions, selective service registration issues, or extended trips abroad. In those cases, the questions on Form N-400 require precise answers, and the consequences of an incorrect answer can include denial, referral to removal proceedings, or a finding of fraud that bars future immigration benefits.

If you answer "yes" to any question in Part 12 of Form N-400 (questions about criminal history, immigration violations, false claims to citizenship, or failure to support dependents), consult an attorney before you file. The naturalization interview is under oath — an inconsistent or incomplete answer to a Part 12 question can result in denial or worse. An attorney can evaluate the record, determine whether the issue is a bar to naturalization, and help you prepare the evidence and explanation USCIS will require.

The Law Offices of Peter D. Chu offers initial consultations to evaluate N-400 eligibility and filing readiness.

Disclaimer: This article provides general information about USCIS Form N-400 filing procedures and mailing addresses. It is not legal advice and does not create an attorney-client relationship between you and the Law Offices of Peter D. Chu or any attorney. Immigration outcomes depend on individual facts, and the accuracy of information provided to USCIS. Consult a licensed immigration attorney before filing any application with USCIS to confirm your eligibility and ensure your application is complete and accurate.

Schedule a consultation with the Law Offices of Peter D. Chu — 4615 Convoy St, San Diego, CA 92111 · 858-268-8823 · Mon–Fri, 8:30 AM–5:30 PM. Consultation fee: $250.