15 ILCS 305/9
Whenever any bill, which shall have passed both houses of the General Assembly, shall be returned by the Governor, with his objections thereto, and, upon reconsideration, shall pass both houses by the constitutional majority, it shall be authenticated as having become a law, by a certificate thereon, to the following effect, viz.: "This bill having been returned by the Governor, with his objections thereto, and after reconsideration having passed both houses by the constitutional majority, it has become a law this .... day of ...., A.D. ....." Which, being signed by the president of the Senate and speaker of the House of Representatives, shall be deemed a sufficient authentication thereof, and the bill shall, thereupon, be deposited with the laws in the office of the Secretary of State.
15 ILCS 305/9