You should begin by discussing your assessment with your township assessor. This is the most efficient and effective way to begin the process of discovery. If you cannot come to an agreed upon value with your assessor you may file an appeal with the Henry County Board of Review. There are generally three bases for appealing an assessment:
Discrepancy in Physical Data
"The Property Record shows I have a 2,500 square foot house, but it's only 2,200 square feet."
"The equalized assessed value is more than 1/3 of my property's fair cash value."
"My equalized assessed value is more than comparable properties in my neighborhood."
The Illinois Property Tax Appeal Board has consistently ruled that the amount of taxes paid or the percentage of change in value from one year to the next is not a valid basis for an appeal.