If you are a non-citizen of the U.S. and wish to find out what materials are in your immigration files, you should file what is known as a "Freedom of Information Act" or FOIA request. This will yield a copy of everything the U.S. Citizenship and Immigration Services (USCIS) has on you. This information is always good to have in advance of filing for any type of immigration benefit - green card, visa, U.S. citizenship, etc.
In fact, if you consult an immigration attorney, he or she is likely to make a FOIA request as one of the first steps in your case -- just to make sure that you haven't forgotten about some earlier run-in with the immigration authorities, or misunderstood an aspect of your previous immigration history.
Every person has a legal right under the FOIA to the contents of his or her own file. However, you cannot simply request another person's FOIA file on your own -- unless you first obtain that person's written consent and signature.
To make a FOIA request from USCIS, you have a few options. The fastest and easiest is probably to use the Department of Homeland Security (DHS)'s online request form, available for free on the DHS FOIA Request Submission Form page of its website.
Another option is to either prepare your own letter or fill out and submit Form G-639, which is available for free download from the USCIS website, and mail, email, or fax your request straight to USCIS.
The G-639 form asks for personal information such as your name, Alien Registration Number (A#) and birth date. This is all to help it locate your file and confirm that it is yours. If you elect not to use the form, but instead prepare your own letter, you should supply as much of the information requested on the form as possible.
Regardless of which USCIS office actually holds your file, you are expected to submit this request to the National Records Center (NRC) in Missouri. You will find the address on the Form G-639 page of the USCIS website.
Thanks to U.S. FOIA laws, you should not have any trouble obtaining your case file.
But you may have to wait several weeks for USCIS to copy and send it to you. To check on the latest processing times, or the status of your own request, go to the Check Status of Request page of the USCIS website.