On Form I864, petitioners must prove that they have the ability to financially support the visa applicant(s) if necessary. In this article, we'll explain how to prove US domicile as part of your Affidavit of Support so you can successfully sponsor a family member for a green card.In this post, we'll explore examples of proof of US domicile and the documents required to establish proof of domicile. How Can I Prove U.S. Domicile? This form is used to precisely document your citizenship, domicile, and tax status. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile.