How to check the Service Area of a field office though?
1. Go to https://egov.uscis.gov/crisgwi/go?action=offices.type&OfficeLocator.office_type=LO
2. Type in your zipcode or your state
3. In the list of Field offices for your state chose any office you need to check
4. Locate "Service Area" in the information provided for this particular office.