Illinois Certificate of Mailing and/or Publication is a document that is used to prove that something was mailed or published. It is a document that is issued by the State of Illinois and is used to provide evidence that the item was actually mailed or published. The certificate serves as proof that the item was sent and/or published in a timely manner. There are two types of Illinois Certificate of Mailing and/or Publication: 1) Certificate of Mailing and 2) Certificate of Publication. The Certificate of Mailing is used to prove that something was mailed to a particular address on a specified date. The Certificate of Publication is used to prove that something was published in a newspaper or other publication on a specified date. Both certificates provide proof of mailing or publishing and are required for certain legal proceedings.