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.This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. This guide will explain how to prove domicile when filling out Form I-864 ("Affidavit of Support"). Consular processing support without the high price tag. Proof of U.S. domicile is required for the I864. Learn examples of proof of domicile along with proof of domicile documents required. 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. Fill out your information, and answer the questions about your home.