Illinois Statutes Chapter 5. General Provisions § 70/1.25. Filing or payment by mail, effective dates--Duplicate filing or payment after notification of mail not received--Registered mail, certified mail, and certificate of mailing as evidence

(1) if transmitted through the United States mail, shall be deemed filed with or received by the State or political subdivision on the date shown by the post office cancellation mark stamped upon the envelope or other wrapper containing it;

(2) if mailed but not received by the State or political subdivision, or if received but without a cancellation mark or with the cancellation mark illegible or erroneous, shall be deemed filed with or received by the State or political subdivision to which it was required or authorized to be directed on the date it was mailed, but only if the sender establishes by competent evidence that the writing or payment was deposited, properly addressed, in the United States mail on or before the date on which it was required or authorized to be filed or was due. In cases in which the writing or payment was mailed but not received, the sender must also file with, or pay to, the State or political subdivision to which the writing or payment was required or authorized to be directed, a duplicate writing or payment within 30 days after written notification is given to the person claiming to have sent the writing or payment, by the State or political subdivision to which the writing or payment was required or authorized to be sent, of its non-receipt of the writing or payment.

If a writing or payment is sent by United States registered mail, certified mail or certificate of mailing, a record authenticated by the United States Post Office of such registration, certification or certificate shall be considered competent evidence that the writing or payment was mailed. The date of registration, certification or certificate shall be deemed the postmarked date.

Notwithstanding any other provision of law, neither a petition for nomination as a candidate for political office nor a petition to submit a public question to be voted upon by the electors of the State or of any political subdivision or district may be considered filed until it is received by the political subdivision, election authority, or the State Board of Elections, as applicable.