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). The household member, other than the immigrant(s) you are sponsoring, must complete and sign Form I-864A, Contract Between Sponsor and Household Member.If you're planning to petition a family member for a green card, you'll most likely need to prepare Form I864, Affidavit of Support. This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile. Download a proof of residency letter template for family members, notarized or non-notarized, tailored for legal use. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States.