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). Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support.Some types of evidence you can share to show you intend to establish domicile include: Opening a bank account. Transferring money to a United States account. Country of Domicile enter the joint sponsor's country of domicile (most sponsors will enter "US" as the country of their domicile). 6. Completing and signing Form I-864 makes you the sponsor.