735 ILCS 5/9-104
The demand required by Section 9-102 of this Act may be made by delivering a copy thereof to the tenant, or by leaving such a copy with some person of the age of 13 years or upwards, residing on, or being in charge of, the premises; or in case no one is in the actual possession of the premises, then by posting the same on the premises; or if those in possession are unknown occupants who are not parties to any written lease, rental agreement, or right to possession agreement for the premises, then by delivering a copy of the notice, directed to "unknown occupants", to the occupant or by leaving a copy of the notice with some person of the age of 13 years or upwards occupying the premises, or by posting a copy of the notice on the premises directed to "unknown occupants". When such demand is made by an officer authorized to serve process, his or her return is prima facie evidence of the facts therein stated, and if such demand is made by any person not an officer, the return may be sworn to by the person serving the same, and is then prima facie evidence of the facts therein stated. The demand for possession may be in the following form:
To ....
I hereby demand immediate possession of the following described premises: (describing the same.)
The demand shall be signed by the person claiming such possession, his or her agent, or attorney.
735 ILCS 5/9-104