815 ILCS 115/6: Guarantor liability.

When a guarantor has agreed in writing that the guarantor is not released by a judgement, settlement, release, or other discharge of indebtedness of the primary obligor, other guarantor, or third party liable on the indebtedness, then the judgment, settlement, release, or other discharge of indebtedness of the primary obligor, other guarantor, or third party liable on the indebtedness shall not release or limit the claim on the indebtedness, or cause the forfeiture, discharge, or extinction of the claim on the indebtedness, against the guarantor, provided that the plaintiff shall not be entitled to more than full satisfaction of his, her, or its claim.