These additional financial sponsors also have to submit an Affidavit of Support, proof of their income, and proof of their legal status in the United States. 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).An I864 sponsor must be domiciled in the United States. Country of Domicile enter the joint sponsor's country of domicile (most sponsors will enter "US" as the country of their domicile). 6. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States.