Illinois Affidavit of Domicile Form. Illinois Affidavit of Residence Form.Use our Affidavit of Residency form to verify your home address for official purposes. How do I fill this out? Your completed and signed form must be filed with the employing withholding agent. Note: Instead of completing this form, you may file a certificate of in-state. Forms on this website are PDFs with fillable fields. Forms should be downloaded to your computer before filling in the fields. The department may ask you to fill out a Legal Residence (Domicile) ​Questionnaire​ to determine your domicile. Applicable Laws and Rules.