Roughly 1,000 DuPage taxpayers who qualify for a senior freeze exemption won’t see it applied on their tax bills next week because of an error by the county.

More homeowners 65 or older are eligible for the Senior Citizens Assessment Freeze Homestead Exemption because state lawmakers last year increased the annual income cap for qualifying residents to $65,000 from $55,000. The program “freezes” the equalized assessed value, generally at a level the year before someone applies and qualifies.

But DuPage Supervisor of Assessments Craig Dovel said his staff discovered Wednesday that the new threshold for the senior property tax exemption wasn’t applied to the records of roughly 1,000 seniors who earn $55,000 to $65,000 a year.

“Due to an error in the computer system, the group of seniors now eligible under the new, higher income threshold, will not see the exemption reflected on the first installment of their property tax bill,” Dovel said in a statement.

Residents can expect their property tax bills to arrive around May 1. Payments are due in equal installments in June and September.

Affected taxpayers will be getting a revised tax bill in July that includes the exemption. Dovel said the adjustment will reduce the amount of the second installment, which is due on Sept. 3.

“Therefore, all property tax bill recipients should pay their first installment,” Dovel said, “and any difference in the appropriate assessment will be reflected in the second installment.”

He said affected residents will receive a letter explaining the process. “We regret the error,” Dovel said. “We are working to ensure this will not be a problem moving forward.”

For details, call the supervisor of assessments office at (630) 407-5858.