Illinois affidavit Of Service By Posting is a legal document used to prove that legal documents have been served upon a party in a court case. This type of affidavit is used when a party must be served with documents but cannot be personally served. The affidavit must be completed and signed by the individual who posted the legal documents, and it must include details such as the date and time of posting, the name of the party who was served, and the address to which the documents were sent. There are two types of Illinois affidavit Of Service By Posting: Certified Mail and Regular Mail. Certified Mail requires the sender to obtain a return receipt, which serves as proof of service. Regular Mail does not require a return receipt, but the sender must still fill out an affidavit of service.