CHICAGO (CBS 2) – Your property taxes are due this week. But some some owners are paying less than they should be and that means you could be paying more. 2 Investigator Pam Zekman first reported on these tax errors last year and the assessor’s office was supposed to correct them. So what happened?

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The agency has reviewed thousands of parcels listed as vacant land and picked up many that were not really vacant. For example one huge home on the city’s southwest side was listed as vacant land for the last two years. And a commercial building that has housed two banks in Orland Park was incorrectly assessed as vacant land for the last five years.

“That’s just outrageous,” said Tony Monahan during an interview just after she paid her elderly mother’s property taxes. It’s also unfair because other taxpayers wind up having to pay for the mistakes. “How can this go on for this length of time in the Assessor’s office.”

Prompted by our reports more than a year ago, former Cook County Assessor James Houlihan asked the 30 township assessors to review thousands of parcels listed as vacant land to be sure they are actually vacant. We rode along with one of them, Niles township assessor Scott Bagnell as he worked on his assignment. And we found several obvious problems, like a huge home in Lincolnwood.

“It’s not vacant land,” Bagnell said. “Obviously it’s a brand new house.”

Former Cook County Assessor James Houlihan previously said he hoped his so called Vacant Land Project would be complete by April. But now we’ve learned that came to a screeching halt just before last November’s Election.

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“What we found, when we first came in was that the project had ceased to exist,” said the current assessor Joseph Berrios. “The field people who were here in the office were assigned to other duties, so we re-instituted it.”

Now Berrios says he has 47 people checking out more than 26,000 suburban properties and also vacant land sites in Chicago to review. “It’s a huge process but we want to make sure that everyone is fairly assessed and no one pays more than their fair share of property taxes.”

We’ve learned that so far suburban buildings with a market value of more than $80 million have been correctly assessed as a result of the vacant land project.

That’s good news to taxpayers lake condo owner Jack Steiner. “You’ve motivated them. Maybe we’ll get people paying the proper tax. Good for you Pam.”

Not so good for property owners who can be back taxed up to four years if mistakes like these are found.

The owners of that Chicago home and Orland Park building say they pay whatever property tax bills they are sent and were not responsible for the assessment errors.

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Click here and you can look up tax assessment information. If you find discrepancies the Assessor’s office urges you to report them.