Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support. 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).Examples of acceptable evidence. Description. Residence in the U.S.. Lease agreement; Mortgage payments; Utility bills. Domicile is determined as of the first day of the session in which a student is attending that semester. 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. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. Completing and signing Form I-864 makes you the sponsor.