When you file an application with USCIS, you will receive a 13-character case number. This is known as the receipt number, and it’s unique to your case.
Your USCIS receipt number will be found on the receipt notice you get when USCIS receives your application. Usually, after you submit an application or petition with USCIS, you should get a receipt notice that informs you that the application was received. So, you will receive an update on a form known as Form I-797C, Notice of Action. The Notice of Action will be sent to the mailing address you listed on the application you submitted. The receipt notice is not a piece of evidence that your immigration benefits have been granted, though. It merely informs you that the application safely made it into the hands of the USCIS officers.
You will be able to find it at the top left corner of the notice. It will start with three letters, either “LIN”, “EAC”, “IOE”, “WAC”, “MSC”, “NBC” or “SRC”. After the letters, there will be ten numbers. The receipt number will let you check out the status of your application. The receipt number is made of the USCIS service center that processed your application, as well as the fiscal year and workday when the case was opened by USCIS. Furthermore, it also contains your unique case number.