If you live in Nassau County, you might want to check your tax bill. Hundreds of Nassau property owners incorrectly received higher tax bills.

The error affects at least 800 families in different districts all over the county and it was all discovered because a Levittown man refused to believe that his taxes could jump 17% in one year.

"I immediately saw that it went up over a thousand bucks. I was like that doesn't look right," said Scott Diamond of Levittown.

After taking a closer look at his tax bill, Diamond realized that the Nassau County Department of Assessment miscalculated his Taxpayer Protection Program (TPP) exemption amount.

Diamond should have had a 40% exemption on the increase in equalized assessed value from the 2020-2021 reassessment. Instead, his tax bill reflected a 4% exemption and resulted in a $1,182 increase in taxes.

"The explanation I got was that it had something to do with physical changes to the property, except I haven't had any physical changes to my property," Diamond said.

Homeowners across the county were shocked to open their bills and find an unexpected tax increase. In Plainview, Louise Mund said her tax bill jumped more than $1,500.

"A very big increase considering we grieve our taxes," Mund said. "People are getting older and it's going to be harder to pay the taxes, but even in general it just doesn't seem fair."

Diamond brought the error to the attention of county leaders. Nassau County Legislature Minority Leader Kevan Abrahams said tax representatives reviewed records and found at least 800 errors. He said this is part of an ongoing problem.

"We have heard cases where people have seen their taxes skyrocket to the tune of $15,000 more than what they should be paying," said Abrahams. "That to me is unbelievable."

A spokesperson for the Minority Caucus refused to say which tax company they worked with to review the tax records and ultimately discovered widespread errors, telling News 12 they could not reveal their source.

The problem is now being addressed by the Department of Assessment and 800 people should be getting lower tax bills in the mail.

"Upon careful review of the methodologies and formulas that were used for the TPP, the Department of Assessment discovered a human error had occurred when a manual calculation was applied to some properties for the 2022-2023 tax year," Matt Cronin, acting assessor, said in a statement. "The Department of Assessment addressed the issue and the correct TPP calculation has now been applied on the new updated 2022-2023 tax bill."

A Nassau County spokesperson said the employee responsible for the error has been disciplined.

Diamond is anxiously awaiting his new tax bill in the mail. His payment due date is quickly approaching and he said he'll be forced to pay the wrong bill to avoid consequences.

"I don't want to go into tax arrears. I don't want to incur late charges so I have no real choice," Diamond said. "I have to count on the county to rectify the error and, if they can't in time, provide refunds."

A county spokesperson told News 12 that no taxpayers have paid the wrong amount yet, so they have not had to provide any refunds.

How can you see if you were overbilled? Check the number listed as your exempt amount on your tax bill. Diamond said that number should be half of what it was on your 2021 tax bill. If you don't have your tax bill handy, you can find that information by entering your address here.