Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support. This affidavit is a contract between a sponsor and the U.S. Government.Completing and signing Form I-864 makes you the sponsor. 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). APPLICANTS SEEKING IN-STATE STATUS AS A MARYLAND RESIDENT MUST COMPLETE THIS ENTIRE FORM, INCLUDING ALL THE FOLLOWING. Download a proof of residency letter template for family members, notarized or non-notarized, tailored for legal use. Students are required to sign a statement verifying their residency claims. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States.