765 ILCS 5/24
No judge or other officer shall take the acknowledgment of any person to any deed or instrument of writing, as aforesaid, unless the person offering to make such acknowledgment shall be personally known to him to be the real person who and in whose name such acknowledgment is proposed to be made, or shall be proved to be such by a credible witness, and the judge or officer taking such acknowledgment shall, in his certificate thereof, state that such person was personally known to him to be the person whose name is subscribed to such deed or writing, as having executed the same, or that he was proved to be such by a credible witness (naming him), and on taking proof of any deed or instrument of writing, by the testimony of any subscribing witnesses, the judge or officer shall ascertain that the person who offers to prove the same is a subscribing witness, either from his own knowledge, or from the testimony of a credible witness; and if it shall appear from the testimony of such subscribing witness that the person whose name appears subscribed to such deed or writing is the real person who executed the same, and that the witness subscribed his name as such, in his presence and at his request, the judge or officer shall grant a certificate, stating that the person testifying as subscribing witness was personally known to him to be the person whose name appears subscribed to such deed, as a witness of the execution thereof, or that he was proved to be such by a credible witness (naming him), and stating the proof made by him; and where any grantor or person executing such deed or writing, and the subscribing witnesses, are deceased or cannot be had, the judge or officer, as aforesaid, may take proof of the handwriting of such deceased party and subscribing witness or witnesses (if any); and the examination of a competent and credible witness, who shall state on oath or affirmation that he personally knew the person whose handwriting he is called to prove, and well knew his signature (stating his means of knowledge), and that he believes the name of such person subscribed to such deed or writing, as party or witness (as the case may be), was thereto subscribed by such person; and when the handwriting of the grantor or person executing such deed or writing, and of one subscribing witness (if any there be), shall have been proved, as aforesaid, or by proof of signature of grantor where there is no subscribing witness, the judge or officer shall grant a certificate thereof stating the proof aforesaid.
765 ILCS 5/24