USCIS uses this number to track an immigrant’s file within USCIS.
This article discusses what an Alien Registration Number is, why USCIS assigns an Alien Registration Number, and where this number is found on a variety of USCIS documents.
Alien Registration Number – What is it?
Alien Registration Numbers is an eight- or nine-digit number USCIS assigns to foreign-born persons who seek immigration benefits.
Alien Registration Number is also called “A-Number” or “USCIS Number”.
The purpose of an A-Number is to track all forms and documents related to you through the U.S. immigration system under the USCIS.
Your Alien Registration Number will be assigned when you file your first immigration application with the USCIS.
Every A-Number is unique, and no two people have the same number.
You will use this same USCIS A-Number for the rest of your life.
It is important that you place your A-Number on every form and document you submit to the USCIS, and verify the A-Number is on every document you receive from USCIS – make sure this is the number assigned to you.
Where is My Alien Registration Number Found?
Your unique Alien Registration Number is found on every USCIS-issued notice, document, and card. Examples of where your A-Number can be found on a variety of documents are found below:
USCIS notices (I-797C)
You can find you A number in Notices of Action (I-797C) USCIS mailed to you.
For example, in the USCIS Notice of Action below A number can be found in “USCIS Alien Number” field.
Also A number can be found in “USCIS A#” part of the notice.
Permanent Resident Card (Green Card)
A green card, officially known as a Permanent Resident Card, is the document issued by the USCIS to immigrants under the Immigration and Naturalization Act to prove you are a lawful permanent resident of the United States.
Your A-Number on the permanent resident card is circled in yellow.
Employment Authorization Card
Every U.S. employer must verify that a prospective employee is authorized to work in the United States.
Your Employment Authorization Card (EAD) is proof that you have USCIS permission to work in the U.S.
If you have obtained an immigrant visa to enter the U.S., your visa also has a Registration Number (A number) assigned by the USCIS.
Immigration Court notices
If you have ever been in immigration court, you can find your DHS assigned A number in immigration court notices.
See example below.
Make Sure Your Correct Registration Number is on Everything
The bottom line is to make sure your proper USCIS Alien Registration Number is on every document you file and on every document you receive.
Further Information about the A-Number on USCIS.
USCIS Case Processing Times 
Green Card Renewal – Complete Guide