If you own property in Cook County, there’s one number you should always know: your PIN.

That’s short for Property Index Number—a 14-digit code assigned to every piece of real estate in the county. It’s tied to the legal description of your property and is used for assessments, tax rates, exemptions and collections. Whether you own a house, a vacant lot, a parking space or a condominium, your property has a PIN.

Think of it as the Social Security number for your home. And just like with your Social Security number, using the wrong one can cause major problems.

If you don’t pay on the right PIN—you haven’t paid your taxes. You’ve just paid someone else’s. That means your property would be marked delinquent, and you might not even know it until it's too late.

You can find your PIN on any property tax bill. If you recently bought your home or purchased it years ago, it should be on your deed. If it’s not on the deed, go to cookcountytreasurer.com, click the purple box and enter your address. You’ll see a photo of your property and your correct PIN.

Still think you don’t need to know your PIN? If your mortgage company pays your taxes through an escrow account, you might assume everything is being handled. But you should still double-check. Knowing your PIN allows you to verify that taxes are being paid in full, on time, and—most importantly—on the correct property.

In another scenario you might be sharing a PIN with other owners. That happens with newly built homes, condos or townhouses that haven’t yet been subdivided. If someone else with whom you share a PIN fails to pay their share, the whole PIN can go delinquent—and your property can be at risk even if you paid your entire portion.

If that’s the case, contact the Cook County Assessor’s Legal Department to find out how to make payments by legal description. Doing so ensures you're only paying what you owe—and not footing the bill for a neighbor who has yet to pay.

You’ll also need your PIN if you want to:

• Request a duplicate tax bill
• Check for refunds or your exemption status
• Ask questions about your bill or payment history

And yes, PINs can change. When a property is split, combined or redeveloped, new PINs are assigned. That’s common with new construction, subdivisions and even converted parking spaces. If you just bought a new home or condo, it’s especially important to make sure you’re paying taxes on the correct—and current—PIN.

Bottom line: the PIN is the key to your property’s tax identity. Know it. Use it. And check it online because mistakes can happen, and the longer they’re left to fester, the more expensive they become.