Illinois Code § 2-403

§ 2-403.

Who may be plaintiff - Assignments - Subrogation. (a) The assignee and owner of a non-negotiable chose in action may sue thereon in his or her own name. Such person shall in his or her pleading on oath allege that he or she is the actual bona fide owner thereof, and set forth how and when he or she acquired title. The action is subject to any defense or set-off existing before notice of the assignment. (b) In all cases in which the chose in action consists of wages due or to become due to the assignor thereof from the defendant in the action, at least 5 days' written notice of the pendency of the action shall be served upon the assignor, before the trial of the same. Upon application of the assignor of the chose in action the court shall allow him or her to intervene and be made a party to the action. The assignor, or the defendant to the action on behalf of the assignor, shall be allowed to set up or affirmatively maintain any just setoff, discount or defense which the assignor may have to the assignment of the chose in action, or to the indebtedness, the payment of which is secured by the assignment of the chose in action. The court, by jury or otherwise, shall ascertain the amount of the indebtedness remaining due and unpaid from the assignor to the assignee of the chose in action. The judgment, if any, against the defendant shall not exceed the amount so found to be due and unpaid from the assignor to the assignee of the chose in action. Judgment for the balance, if any, remaining due from the defendant, upon the assigned chose in action, shall be rendered in favor of the assignor and against the defendant in the action or proceeding. The court may enter any order as to costs in the proceeding that may be equitable. (c) Any action hereafter brought by virtue of the subrogation provision of any contract or by virtue of subrogation by operation of law shall be brought either in the name or for the use of the subrogee; and the subrogee shall in his or her pleading on oath, or by his or her affidavit if pleading is not required, allege that he or she is the actual bona fide subrogee and set forth how and when he or she became subrogee. (d) A judgment in an action brought and conducted by a subrogee by virtue of the subrogation provision of any contract or by virtue of any subrogation by operation of law, whether in the name of the subrogor or otherwise, is not a bar or a determination on the merits of the case or any aspect thereof in an action by the subrogor to recover upon any other cause of action arising out of the same transaction or series of transactions. (Source: P.A. 83-707.)