755 ILCS 5/6-21
If a will has been admitted to probate before notice in accordance with Section 6-4, any person entitled to notice under Section 6-10 may file a petition within 42 days after the effective date of the original order admitting the will to probate to require proof of the will pursuant to this Section. The court must set the matter for hearing upon such notice to interested persons as the court directs. At the hearing the proponent must establish the will by testimony of the witnesses as provided in subsection 6-4 (b) (1) or Section 6-5 or other evidence as provided in this Act, but not as provided by subsection 6-4 (b) (2) or subsection 6-4 (b) (3), as if the will had not originally been admitted to probate. If the proponent establishes the will by sufficient competent evidence, the original order admitting it to probate and the original order appointing the representative shall be confirmed and are effective as to all persons, including creditors, as of the dates of their entries, unless there is proof of fraud, forgery, compulsion or other improper conduct, which in the opinion of the court is sufficient to invalidate or destroy the will. The time for filing a petition to contest a will under Section 8-1 is not extended by the filing of the petition under this Section if the order admitting the will to probate is confirmed, but if that order is vacated, the time for filing the petition under Section 8-2 runs from the date of vacation of the order admitting the will to probate.
755 ILCS 5/6-21