Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support. If you want to sponsor someone for a family-based green card, you need to provide proof of a U.S. domicile in your Affidavit of Support (Form I-864).US Passport or US Passport Card 2. An interactive checklist to help prepare you for the application process. Follow the steps indicated at the top of each page. Download a proof of residency letter template for family members, notarized or non-notarized, tailored for legal use. For an independent student to be considered a resident of Illinois they must have physically resided in Illinois for 12 continuous full months. NOTE: The requirement is to verify Illinois residency, not a person's address of record.