Learn how to prove your U.S. domicile for a family visa with our stepbystep guide. Essential documents and tips to ensure visa approval.Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. 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. This guide will explain how to prove domicile when filling out Form I-864 ("Affidavit of Support"). Consular processing support without the high price tag. 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). One of the requirements for Form I864 is showing that you are domiciled in the US. In other words, your principal residence must be located in the US. Completing and signing Form I-864 makes you the sponsor. There are several requirements to submit an I864 Affidavit of Support.