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). Download and complete the Declaration Of Domicile Florida (PDF) form.Proof must show street address; Post Office boxes are NOT acceptable proof for determining residency. This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile.