Illinois splits the answer by who is paying. A diminished value claim in Illinois works against the at-fault driver, while a claim on your own policy has already lost in court.
Trailmobile and the Repaired Condition
The key case is Trailmobile v. Higgs, an appellate decision from 1973. It set the measure as the gap in market value before the injury and in the repaired condition. That gap is the lost value, and it comes on top of the repair bill.
The MWL chart of all 50 states lists Trailmobile as the Illinois rule for claims against the person who caused the damage. To use it, you need a number for the car as fixed. Most owners get one from a diminished value appraisal and then send a demand letter.
Sims Closed the Door on Your Own Policy
In 2006, an Illinois appeals court decided Sims v. Allstate. The policy promised repair with parts of like kind and quality. Reading an intangible lost value element into that promise, the court said, would ignore the policy's language. Your own collision claim stops at the repair.
Five Years, But Fault Can End It
Illinois gives you five years to sue for injury done to property under 735 ILCS 5/13-205. Few claims take that long, yet the time helps when an insurer drags out talks for months.
Your share of the blame matters more. The fault rule in 735 ILCS 5/2-1116 tells the court to deny recovery if your fault is more than 50%. At or below that point, the award is cut by your percentage.
Coverage Floors and Small Claims
Under the Illinois Department of Insurance shopping guide, drivers need property damage limits of at least $20,000 per accident. A serious crash on a late model car can push repair and lost value past that total.
The small claims limit in Illinois is $10,000, according to a circuit court FAQ. Smaller lost value claims belong there. When an insurer stops returning calls, use the department's complaint page. For the opposite rule on your own policy, look at Georgia. Next door, Indiana is much closer to Illinois.