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).You must live in the United States or a U.S. territory and have proof of domicile. Must meet the financial requirements. This tool is to assist you in determining what, if any, financial evidence you submit with your Affidavit of Support. Under required documents for joint sponsor on CEAC is a spot for PROOF OF US DOMICILE. USCIS requires Form I864, Affidavit of Support, for most familybased applications and some employmentbased applications.