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). Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States.Examples of acceptable evidence. Description. Residence in the U.S.. Lease agreement; Mortgage payments; Utility bills. In this post, we'll explore examples of proof of US domicile and the documents required to establish proof of domicile. There are several requirements to submit an I864 Affidavit of Support. The proof of U.S. domicile is one of those required documents. A declaration is a simple statement that you intend in good faith to return to the United States to resume your domicile.