810 ILCS 5/2A-206

Offer and acceptance in formation of lease contract.

(1) Unless otherwise unambiguously indicated by the language or circumstances, an offer to make a lease contract must be construed as inviting acceptance in any manner and by any medium reasonable in the circumstances.

(2) If the beginning of a requested performance is a reasonable mode of acceptance, an offeror who is not notified of acceptance within a reasonable time may treat the offer as having lapsed before acceptance.