Section 735 ILCS 5/2-608 - Counterclaims(a) Any claim by one or more defendants against one or more plaintiffs, or against one or more codefendants, whether in the nature of setoff, recoupment, cross claim or otherwise, and whether in tort or contract, for liquidated or unliquidated damages, or for other relief, may be pleaded as a cross claim in any action, and when so pleaded shall be called a counterclaim.(b) The counterclaim shall be a part of the answer, and shall be designated as a counterclaim. Service of process on parties already before the court is not necessary.(c) Every counterclaim shall be pleaded in the same manner and with the same particularity as a complaint, and shall be complete in itself, but allegations set forth in other parts of the answer may be incorporated by specific reference instead of being repeated.(d) An answer to a counterclaim and pleadings subsequent thereto shall be filed as in the case of a complaint and with like designation and effect.