An affidavit is the written equivalent of verballygiven court testimony. An affidavit is more than just a legal document; it's a sworn statement that holds significant weight in the eyes of the law.An affidavit of marriage is a legally binding document that proves a legal marriage exists between two people. If you live outside of Illinois, the clerk may ask you to sign an affidavit stating that your home state does not declare your marriage void. The first step to the formal, legal process of divorce in Illinois is filing the Petition For Dissolution of Marriage. An affidavit is a written statement made under oath that is typically used in legal proceedings. Learn their purpose, when to use, and how to write. Supreme Court Rule 191 affidavits and suggests how to attack an affidavit for failing to comply with the rule. I. The Comprehensive Financial Affidavit and any financial documents shall not be filed. 3. Filing a Petition For Dissolution of Marriage starts the formal divorce process in Illinois.