The huge backlog of appeals from Marion County homeowners challenging their property tax bills is about to get even bigger.

County homeowners who received assessment notices Dec. 14 have until Monday to file an appeal, and the Marion County assessor’s office is bracing for the onslaught.

The office already has 27,000 appeals outstanding from as far back as 2008 and is expecting at least 10,000 more from the 2012 assessment, adding to the logjam that has vexed the office for years.

“Marion County will never have zero appeals,” Assessor Joseph O’Connor said. “That’s like saying the courts will have no cases. The way the law is set up makes it impossible.”

The assessor’s office has seen its number of appeals grow since 2006, when all 360,000 parcels of land were reassessed under orders from the state.

Property tax bills spiked following statewide reassessment in the summer of 2007 and sparked large public protests. As a result, then-Gov. Mitch Daniels ordered another assessment the following year of all Marion County properties. Those assessements started a backlog that the assessor’s office has yet to dig out of.

The assessor’s office received a record 22,000 appeals of the 2006 reassessment, O’Connor said. The number grew to as high as 32,000 in the following years before dropping to the current 27,000.

O’Connor has set a goal to resolve previous appeals by the end of this year.

If he’s successful, that would leave only the appeals due Monday from the 2012 assessment.

“We’re expecting a lot of appeals,” O’Connor said. “There’s a lot of confusion, being that it’s a reassessment year.”

The assessor’s office is expecting more appeals that normal from the 2012 assessment because it’s the first “true” assessment county assessors have conducted since 2002. That’s when the state switched from a “true-tax value” to a “market-based” assessment.

Assessments were typically conducted every 10 years. But following the 2002 switch, the legislature ordered assessors beginning in 2006 to update property values every year using the trending method to more accurately reflect values until another assessment could be conducted in 2012.

Trending bases property tax amounts on prices that properties in a particular area have sold for during the past two years to estimate values rather than using a formula to set a value based on different features of a property.

But when property is so seldom truly reassessed, the assessment changes that occur in the meantime can be substantial and prompt more appeals.

“We have cases pending as far back as 2006, so [the county's backlog] is not surprising,” said Stephen Paul, a partner at the Faegre Baker Daniels LLP law firm.

The state legislature now has mandated assessments be done every four years instead of 10, making it even harder for the Marion County assessor’s office to work through the mountain of appeals.

Further, filing an appeal has been simplified in recent years as homeowners no longer are required to fill out a complicated form to protest their bill. They simply need to express their wish to file an appeal in writing.

That’s prompted O’Connor to encourage people “to call in before just filing a blind appeal” hoping that some disagreements may get settled without an official filing.