To win an unjust enrichment claim in Illinois, a plaintiff must prove the elements the Illinois Supreme Court laid out in HPI Health Care Services, Inc. v. Mt. Vernon Hospital, Inc.: the defendant unjustly retained a benefit to the plaintiff’s detriment, and that retention violates the fundamental principles of justice, equity, and good conscience.1Justia. HPI Health Care v Mt Vernon Hosp Courts usually break that two-part rule into three practical questions when they analyze a case.
The Three Elements a Plaintiff Must Prove
A Benefit the Defendant Received
The plaintiff has to show the defendant received something of measurable value. A cash payment. Professional services. Use of property. A reduction in the defendant’s debts. Anything that concretely increases the defendant’s net worth can qualify, but the evidence has to be concrete too: bank records, invoices, delivery confirmations, testimony that work was performed. Abstract or speculative benefits will not carry the claim.
Detriment to the Plaintiff
The benefit cannot exist in a vacuum. The defendant’s gain must have come at the plaintiff’s expense. In direct dealings this is easy to see: the plaintiff paid money, delivered goods, or performed work, and the defendant kept the value without paying for it.
When a third party is in the middle, the connection is harder to draw. The HPI court identified three situations where retention still counts as unjust even though the benefit passed through someone else: the benefit was supposed to go to the plaintiff but got misdirected by mistake, the defendant obtained it through wrongful conduct, or the plaintiff simply had a better legal claim to it than the defendant did.1Justia. HPI Health Care v Mt Vernon Hosp
Retention That Violates Justice, Equity, and Good Conscience
This is where courts have the most discretion and where plaintiffs run into the most trouble. Even a clear benefit received at the plaintiff’s expense is not enough on its own. The plaintiff still has to show that letting the defendant keep it would be fundamentally unfair. Judges look at how both sides behaved, the circumstances of the transfer, and whether the defendant has any legal justification for holding on to the benefit. A bad deal by itself does not satisfy this element. The question goes past accounting into basic fairness.
What Makes Retention “Unjust”
Illinois courts have never settled on a single clean answer, and the disagreement matters. Some courts require the plaintiff to point to specific wrongful conduct by the defendant, such as fraud, duress, or breach of fiduciary duty. On that reading, unjust enrichment is essentially a tag-along theory that depends on proving an independent wrong. Other Illinois courts read the doctrine more broadly and allow claims without underlying wrongdoing, so long as the circumstances make retention inequitable.
HPI itself supports the broader reading. The Supreme Court described unjust enrichment as reaching situations where a defendant “wrongfully secured or passively received” a benefit that would be unconscionable to keep.1Justia. HPI Health Care v Mt Vernon Hosp The phrase “passively received” suggests the defendant need not have done anything wrong. But several appellate decisions have read the doctrine more narrowly, insisting on some identifiable wrongdoing like fraud or undue influence. Which line of authority a judge follows can decide whether a claim survives a motion to dismiss.
Factual triggers courts on both sides of the split tend to accept include:
- Fraud or misrepresentation, where the defendant secured the benefit by lying about material facts.
- Duress or coercion, where the plaintiff transferred value under threat or pressure.
- Mistake of fact, such as a homeowner paying a contractor for work that was accidentally performed on a neighbor’s property.
- Passive receipt of a benefit the plaintiff expected to be paid for, with no legal right on the defendant’s side to retain it.
Can the Claim Stand on Its Own
This question is contested in Illinois, and getting it wrong can kill a case. Some appellate courts treat unjust enrichment as an independent cause of action with its own elements, meaning a plaintiff can bring it without also proving fraud, breach of contract, or another separate theory. Other appellate courts have held the opposite: that unjust enrichment is not a standalone claim and must be tied to an underlying wrong.
The Illinois Supreme Court’s own language leans toward independence. In Raintree Homes, Inc. v. Village of Long Grove, the court acknowledged that plaintiffs had “no substantive claim grounded in tort, contract, or statute” and that “the only substantive basis for the claim is restitution to prevent unjust enrichment.” That reasoning treats the theory as capable of standing alone. Yet decisions in the First and Third Appellate Districts have flatly stated it cannot.
The practical takeaway: plead unjust enrichment alongside other theories whenever the facts allow it, because the district hearing your case may follow the narrower line. If unjust enrichment is your only viable theory, check the recent decisions in the appellate district where the case will land.
When an Express Contract Blocks the Claim
Illinois draws a hard line here. If a valid, enforceable contract already governs the dispute, unjust enrichment is not available. Courts will not imply an obligation in fairness when the parties negotiated their own terms. An express contract, written or oral, defines the relationship, and a party unhappy with the deal has to sue for breach of contract instead.2Illinois Courts. 2019 IL App (1st) 18-0075-U
That bar holds even when the contract turns out to be a bad bargain. Equity will not rewrite terms someone voluntarily accepted. The exception is a contract that is void or unenforceable because of a legal defect. A failed contract cannot define the parties’ rights, and unjust enrichment can step in.
Plaintiffs are allowed to plead unjust enrichment in the alternative to a breach of contract count, which matters because enforceability is often disputed. The catch is that the unjust enrichment count itself cannot incorporate allegations of an express contract. The two counts have to stay in separate lanes: the contract count relies on the contract’s existence, the unjust enrichment count proceeds as if no contract governs.2Illinois Courts. 2019 IL App (1st) 18-0075-U Mixing the two in one count is the kind of drafting mistake that gets claims dismissed.
Deadline to File
Illinois applies a five-year statute of limitations to unjust enrichment claims under 735 ILCS 5/13-205, the catch-all provision covering civil actions not specifically addressed by another limitations period.3Illinois General Assembly. 735 ILCS 5/13-205 The clock generally starts when the cause of action accrues, which typically means when the plaintiff knew or should have known that the defendant was retaining a benefit unjustly.
Five years sounds generous, but waiting has other costs. Evidence disappears, witnesses forget, and courts look skeptically at plaintiffs who sat on a claim for years before asserting it.
What Proving the Elements Gets You
A successful unjust enrichment claim in Illinois produces restitution, not traditional compensatory damages. That distinction matters. Compensatory damages measure what the plaintiff lost; restitution measures what the defendant gained. If the defendant’s unfair gain was $5,000, the judgment targets that figure regardless of whether the plaintiff’s actual loss was higher or lower. The goal is to strip away the unjust advantage.
Restitution usually takes the form of a monetary judgment equal to the fair market value of the benefit retained. When specific property is involved, Illinois courts can also impose a constructive trust, treating the defendant as holding the property in trust for the plaintiff and ordering it returned rather than ordering a payment. The Illinois Supreme Court has held that a constructive trust can be used to prevent unjust enrichment and that wrongful conduct by the defendant is not always required. Because the property is set apart from the defendant’s other creditors, this remedy can be the difference between a paper judgment and an actual recovery when the defendant is in financial trouble.