The Illinois Certificate of Mailing Workers Compensation is a document provided by the Illinois Workers' Compensation Commission (IPCC) to employers and insurance companies in the state of Illinois. It provides proof that a document has been sent to the IPCC or another party. There are two types of Illinois Certificate of Mailing Workers Compensation: the Certificate of Mailing and the Certificate of Service. The Certificate of Mailing is used when documents are sent via regular mail, while the Certificate of Service is used when documents are sent via email or other electronic means. The Certificate of Mailing or Service must be completed and filed with the IPCC within five days of sending the documents. The Certificate must include the date the document was sent, the method of mailing (regular mail, email, etc.), the name and address of the person or entity to whom the documents were sent, and the name and address of the person or entity sending the documents.