How Can I Prove U.S. Domicile? Washington State offers specific templates designed to simplify the process for legally domiciled adults.All domicile must be established at least one year immediately prior to the first day of the quarter the student is seeking residency. 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). You must provide proof of Washington residency using one document that shows your current Washington residence address and your full name. This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile. Establish proof of domicile. Use our Affidavit of Residency form to verify your home address for official purposes.