735 ILCS 5/8-2301
Any person may take the deposition of a witness to perpetuate the remembrance of any fact, matter or thing, relating to the boundaries or improvements of land, the name or former name of water course, the name or former name of any portion or district of the county, the ancient customs, laws or usages of the inhabitants of any part of this country, as far as they may pertain to the future settlement of land claims or the marriage or pedigree of any person, any other matter or thing necessary to the security of any estate, or to any private right by filing a petition supported by affidavit in the circuit court of the proper county. The petition shall set forth, briefly and substantially, the petitioner's interest, claim or title in or to the subject concerning which the petitioner desires to perpetuate evidence, the fact intended to be established, the names of all other persons interested or supposed to be interested therein, whether there are any persons interested therein whose names are unknown to the petitioner (who shall be designated as unknown owners), and the name of the witness proposed to be examined. Except as in this Section otherwise provided, the procedure for the giving of notice to interested persons, including unknown owners, and the manner of taking the deposition shall be that provided by the rules of the Supreme Court now or hereafter in effect for the taking of depositions for the perpetuation of testimony. A deposition taken under this Section may be used as evidence in any case in the same manner and subject to the same conditions and objections as if it had originally been taken in that case. The deposition is admissible against parties notified as unknown owners to the same extent as it is against other notified parties.
735 ILCS 5/8-2301