To locate the USCIS office that’s processing your case, it can be found on your receipt notice. After you mail your application, you will receive a notification from immigration that says form I-797, Notice of Action. Specifically, the example that comes to mind is a lot of people are having confusion over fiancé visas.
For example, you mail your application to a Dallas lock box but Texas is not where your case is being processed. The office where your case is being processed is on the receipt notice that you received. You’ll see at the bottom of the notice where the field office your case is located.
Just because you sent your case to a Chicago lock box or a Texas lock box doesn’t mean that that is your service center. The actual service center is listed on your receipt notice in the bottom left-hand corner.
There are specific cases like the naturalization case, N400, an adjustment of status, I485 and those notices will say the National Benefit Center but that’s actually not where the case is being processed. In those examples, the case will actually be in the field office in the state where you’re residing.