Assessing authorities may use mass-appraisal methods, property characteristics, sales information, neighborhood or property classifications, and scheduled reassessment cycles rather than individually appraising every property each year. The exact process and timing depend on the jurisdiction.
That makes the underlying property record important. If characteristics such as building area, lot size, age or other relevant facts are incorrect, those discrepancies may affect an assessment and deserve review. A difference in the record does not by itself prove that the assessment is wrong.
An assessed value is also not necessarily the same as market value. In Illinois, property is generally assessed as a percentage of market value, subject to jurisdiction-specific rules, and equalization can affect the value used in the property-tax calculation. Exemptions and tax rates are separate parts of the tax calculation.
The useful questions are whether the assessment is supported by the applicable property record and whether relevant evidence — including comparable properties or market evidence where appropriate — provides a basis for further review.