Written by Jennifer Oppliger A Social Security Number (SSN) is a number that identifies U.S. citizens and other selected residents. Noncitizens can generally only receive SSNs if they are employed in the U.S. An SSN is used to track your annual income. The Social Security Administration (SSA) is in charge of the SSN application process. How do I apply for an SSN if I am working on-campus? Receive an on-campus employment letter. Submit an “SSN/ITIN Support Letter” request in MyISSS….