755 ILCS 5/6-5
When a witness to a will or other party who shall testify to have a will admitted to probate resides outside the county in which the will is offered for probate or is unable to attend court and can be found and is mentally and physically capable of testifying, the court, upon the petition of any person seeking probate of the will and upon such notice of the petition to persons interested as the court directs, may issue a commission with the will or a photographic copy thereof attached. The commission shall be directed to any judge, notary public, mayor or other chief magistrate of a city or United States consul, vice-consul, consular agent, secretary of legation or commissioned officer in active service of the armed forces of the United States and shall authorize and require the authorized person to cause that witness or other party to come before the authorized person at such time and place as the authorized person designates and to take the deposition of the witness or other party on oath or affirmation and upon all such written interrogatories and cross-interrogatories as may be enclosed with the commission. With the least possible delay the person taking the deposition shall certify it, the commission, and the interrogatories to the court from which the commission issued. When the deposition of a witness or other party is so taken and returned to the court, the testimony of the witness or other party has the same effect as if the witness or other party testified in the court from which the commission issued. When the commission is issued to the officer by official title only and not by name, the seal of the office attached to the officer's certificate is sufficient evidence of the officer's identity and official character.
755 ILCS 5/6-5