The Illinois Certificate of Mailing is a form that is used to document the date of mailing a document in the state of Illinois. There are three types of Illinois Certificate of Mailing forms available: the Certificate of Mailing Form for Business Entities, the Certificate of Mailing Form for Individuals, and the Certificate of Mailing Form for Notaries. The certificate documents that a document has been placed in the mail after the date and time indicated on the form. Once completed, the form must be signed, dated, and notarized. The Certificate of Mailing Form is available from the Illinois Secretary of State's office.