On Form I864, petitioners must prove that they have the ability to financially support the visa applicant(s) if necessary. 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).How Can I Prove U.S. Domicile? In this post, we'll explore examples of proof of US domicile and the documents required to establish proof of domicile. 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. A declaration is a simple statement that you intend in good faith to return to the United States to resume your domicile. Fill in the name of the Attorney General of the United States. 5.7.4.4. Fill in the name and address for the Secretary of State for your state.