Uninsured vs Underinsured Motorist Coverage in Illinois

If you're paying for auto insurance in Illinois, you're already carrying uninsured and underinsured motorist coverage whether you realize it or not. Illinois law requires it. But most drivers don't understand the difference between the two, and that confusion can cost you thousands of dollars after an accident. Knowing how uninsured vs underinsured motorist coverage works in Illinois helps you make smarter policy decisions and protects you when the other driver can't pay for the damage they caused.

What's the difference between uninsured and underinsured motorist coverage in Illinois?

These two types of coverage sound similar, but they apply in very different situations. Here's the simplest way to think about it:

Uninsured motorist (UM) coverage kicks in when the at-fault driver has no auto insurance at all or when you're hit by a hit-and-run driver who can't be identified.
Underinsured motorist (UIM) coverage applies when the at-fault driver has insurance, but their policy limits aren't high enough to cover your full damages.

So UM protects you from drivers with zero coverage. UIM protects you from drivers who have insurance, just not enough of it. Both are mandatory in Illinois under the Illinois Vehicle Code (625 ILCS 5/7-203), with minimum limits of $25,000 per person and $50,000 per accident.

You can learn more about how uninsured motorist coverage works in Illinois in our detailed breakdown.

Why does Illinois require both types of coverage?

Illinois mandates UM and UIM coverage because the state recognizes a hard reality: a significant number of drivers on the road carry no insurance or carry only the bare minimum. According to the Insurance Research Council, roughly 1 in 8 drivers nationally is uninsured, and Illinois has historically been above average.

Without this required coverage, accident victims would be left to pay their own medical bills, lost wages, and vehicle repairs out of pocket when the at-fault driver can't cover the costs. The state's requirement is designed so that your own policy steps in as a safety net.

How does underinsured motorist coverage actually work after an accident?

Here's a practical example that shows exactly how UIM coverage works:

Imagine you're hit by another driver in Chicago. Your medical bills total $80,000. The at-fault driver carries Illinois's minimum bodily injury liability limits of $25,000 per person. Their insurance pays out its $25,000 maximum, leaving you with $55,000 in uncompensated damages.

If your own underinsured motorist coverage has limits of $100,000 per person, your UIM policy would cover that remaining $55,000 gap subject to your policy's terms. The key point is that UIM doesn't replace the at-fault driver's coverage; it supplements it.

Does uninsured motorist coverage only apply to hit-and-run accidents?

No, but hit-and-run crashes are one of the most common scenarios where UM coverage applies. Uninsured motorist coverage in Illinois covers three main situations:

The at-fault driver has no auto insurance policy whatsoever.
The at-fault driver's insurance company denies coverage or has gone out of business.
A hit-and-run driver injures you and cannot be identified (often called a "phantom vehicle" scenario).

It's worth noting that in hit-and-run cases, most insurers require that there was actual physical contact with the other vehicle. If a driver swerves into your lane, forces you off the road, and flees without contact, some policies may not apply UM coverage. This is an area where understanding what your Illinois policy actually covers can save you a lot of frustration.

What are the minimum UM and UIM limits in Illinois?

Illinois requires a minimum of:

$25,000 bodily injury coverage per person
$50,000 bodily injury coverage per accident

These are the same minimums required for bodily injury liability coverage. However, many insurance professionals recommend carrying higher limits. $25,000 doesn't go far when you're dealing with hospital stays, surgery, rehabilitation, and time off work.

What are the most common mistakes people make with UM and UIM coverage?

Several recurring errors cost Illinois drivers money or leave them underprotected:

Assuming minimum limits are enough. A serious injury can easily exceed $25,000 in medical bills alone. Carrying higher UM/UIM limits is relatively inexpensive compared to liability coverage increases.
Not understanding "setoff" or "reduction" clauses. Some policies reduce your UIM payout by the amount the at-fault driver's insurance already paid. Others pay the full UIM limit on top of the other driver's payment. The wording in your policy matters enormously.
Confusing UIM with collision coverage. UIM covers injury-related damages medical bills, lost wages, pain and suffering. It does not cover vehicle damage. You need collision coverage for that.
Failing to stack coverage. In Illinois, if you have multiple vehicles on your policy, you may be able to "stack" your UM/UIM limits, effectively multiplying your available coverage. Not all policies allow this, so check your declarations page.
Signing a waiver. Illinois law allows you to reject UM/UIM coverage or select lower limits, but only with a written, signed waiver. Some drivers unknowingly sign away this protection when purchasing a policy.

Understanding these key differences between uninsured and underinsured coverage can help you avoid costly gaps in your protection.

How do I file a UM or UIM claim in Illinois?

Filing a claim under your own UM or UIM coverage follows a different process than filing against the other driver's insurance. Here are the general steps:

Report the accident to your insurer promptly. Most policies require timely notice of a potential UM/UIM claim.
Document everything. Get the police report, medical records, witness statements, and photos of the accident scene and injuries.
Establish the other driver's coverage status. For UM claims, you need proof the at-fault driver was uninsured. For UIM claims, you need confirmation of the at-fault driver's policy limits.
Negotiate with your own insurer. This surprises many people, but your UM/UIM claim is essentially a negotiation with your own insurance company and they don't always offer a fair amount.
Consider arbitration or litigation. If your insurer won't offer a fair settlement, many UM/UIM policies include binding arbitration provisions. An attorney experienced in uninsured motorist claims in Illinois can guide you through this process.

Can I increase my UM and UIM coverage after buying a policy?

Yes. You can increase your UM/UIM limits at any time during your policy period by contacting your insurance company or agent. The cost increase is usually modest often just a few dollars per month to raise limits from $25,000 to $100,000 or even $250,000 per person.

One important detail: your UIM coverage limits cannot exceed your underlying bodily injury liability limits. So if you want $250,000 in UIM coverage, you'll need at least $250,000 in liability coverage as well.

For families with multiple drivers or vehicles, reviewing your family uninsured motorist coverage options can reveal ways to maximize protection without dramatically increasing your premium.

Quick checklist: Protecting yourself with the right UM/UIM coverage in Illinois

☐ Review your current declarations page to see your exact UM and UIM limits.
☐ Confirm whether your policy uses "reduction" or "difference" (add-on) UIM language this affects how much you actually receive.
☐ Consider raising your limits above the state minimum of $25,000/$50,000.
☐ Ask your agent about stacking options if you insure multiple vehicles.
☐ Make sure you did not unknowingly sign a waiver rejecting UM/UIM coverage.
☐ Keep copies of your policy documents in a safe, accessible place.
☐ After any accident with an uninsured or underinsured driver, notify your insurer immediately and consider consulting an attorney before accepting any settlement offer.