Article II. Civil Practice · Part 4. Parties · Not amended since adoption on record · Last verified July 20, 2026
In one sentenceSection 2-401 sets the basic naming rules for lawsuits — who is the plaintiff and who is the defendant, how a wrong name gets fixed, and when someone may sue or be sued under a fictitious name.
Full Text of 735 ILCS 5/2-401
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(a)The party commencing an action shall be called the plaintiff. The adverse party shall be called the defendant. (b) Misnomer of a party is not a ground for dismissal but the name of any party may be corrected at any time, before or after judgment, on motion, upon any terms and proof that the court requires.
(c)A party shall set forth in the body of his or her pleading the names of all parties for and against whom relief is sought thereby.
(d)Unless a contrary meaning is indicated, wherever used in this Act and in rules adopted pursuant hereto the term "plaintiff" includes counterclaimants and third-party plaintiffs, and the term "defendant" includes third-party defendants and parties against whom relief is sought by counterclaim.
(e)Upon application and for good cause shown the parties may appear under fictitious names.
Plain-English Summary
The party who starts a case is the plaintiff, and the party on the other side is the defendant. Those two words carry over throughout the case: unless something else is clearly meant, "plaintiff" also covers anyone counterclaiming or bringing a third-party claim, and "defendant" also covers third-party defendants and anyone facing a counterclaim.
Getting a party's name wrong isn't a reason to throw out a case. The name can be corrected at any time, before or after judgment, on motion, and the court can attach whatever terms and proof it thinks the situation calls for. A pleading also has to name, in its body, every party for or against whom it seeks relief.
On a separate note, the section allows parties to appear under fictitious names when they apply to the court and show good cause for it.
Frequently Asked Questions
Who is the plaintiff and who is the defendant in an Illinois civil case?
The party who commences the action is called the plaintiff, and the adverse party is called the defendant. Those labels also reach further into the case — "plaintiff" includes counterclaimants and third-party plaintiffs, and "defendant" includes third-party defendants and parties facing a counterclaim, unless the context clearly means otherwise.
Can a case be dismissed because a party's name was wrong?
No. Misnomer of a party isn't a ground for dismissal. The name can be corrected at any time, before or after judgment, on motion, and the court can set whatever terms and require whatever proof it considers appropriate.
Does a pleading have to name every party it seeks relief from or for?
Yes. A party must set out, in the body of the pleading, the names of everyone for and against whom the pleading seeks relief.
Do the words "plaintiff" and "defendant" cover counterclaims and third-party claims too?
Yes, unless the context clearly indicates otherwise. "Plaintiff" includes counterclaimants and third-party plaintiffs, and "defendant" includes third-party defendants and anyone against whom relief is sought by counterclaim.
Can someone appear in an Illinois lawsuit under a fictitious name?
Yes. On application and a showing of good cause, the parties may appear under fictitious names.
Amendment History
(Source: P.A. 85-907.)
Source & verification. Section text and amendment history are
reproduced verbatim from the Illinois Compiled Statutes, published by the
Illinois Compiled Statutes, Illinois General Assembly / Legislative Reference Bureau. Last verified July 20, 2026.
· Official source
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