From the Franklin County Auditor’s website:
How often does the auditor reappraise?
In Ohio, county auditors are required to do a full general reappraisal once in every six years. This process is called the Sexennial Reappraisal. The Auditor or his qualified appraiser is required to view and appraise every property in the county for this purpose. The process takes between two and two-and-a-half years for a county the size of Franklin to be completed.
On the third year in between reappraisals, each county auditor is required to perform a statistical analysis of the sales which have occurred in the prior three years and provide for a percentage adjustment to be made to the values of all properties in each given marketing neighborhood. These adjustments are also stratified according to value to assure that the equitability of the valuations is maintained or corrected based on the analysis of like comparable sales. This process is called the Triennial Update.
Other than the state mandated reappraisal or update, each Auditor is charged with annually maintenancing the properties which have been found to have changed or are no longer appraised at their fair market value. Most often the change is due to new construction, a change in the physical size or shape of the land, or a demolition or damage to a property.