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). If you're planning to petition a family member for a green card, you'll most likely need to prepare Form I864, Affidavit of Support.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. Learn how to prove your U.S. domicile for a family visa with our stepbystep guide. Essential documents and tips to ensure visa approval. Parents or legal guardians will need to provide the following documents: Proof of Residency in Fairfax County. 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.