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). On Form I864, petitioners must prove that they have the ability to financially support the visa applicant(s) if necessary.This affidavit is a contract between a sponsor and the U.S. Government. Completing and signing Form I-864 makes you the sponsor. To complete Form I864, the petitioner must meet certain requirements. Proof of U.S. domicile is required for the I864. Learn examples of proof of domicile along with proof of domicile documents required.