The real property tax is Ohio's oldest tax. It has been an ad valorem tax – meaning, based on value – since 1825, and the Ohio Constitution has generally required property to be taxed by uniform rule according to value since 1851.

Real property tax rates are levied locally and vary by taxing jurisdiction. The total tax rate for any particular parcel includes all levies either enacted by a legislative authority or approved by the voters of all taxing jurisdictions in which the property is a part. Examples of such jurisdictions include school districts, counties, municipalities, townships, and special service districts. Each unique combination of these taxing jurisdictions creates a separate taxing district.

The Ohio Constitution prohibits governmental units from levying property taxes that, in the aggregate, exceed 1 percent of true value, unless they are approved by voters. This is known in state law as the 10-mill limitation on non-voted or "inside" millage.

Each year, the Department of Taxation calculates effective tax rates based on tax reduction factors that eliminate the effect of a change in the valuation of existing real property on certain voted levies. This law, outlined in R.C. 319.301, was enacted in 1976 by the 111th General Assembly as House Bill 920. Reduction factors are applied to eligible tax rates for each taxing unit, such as a school district, a county, or a municipality.

Reduction factors are only calculated on "carryover" property – meaning, property that is taxed in both the preceding and current year within the same reduction factor class. Therefore, new construction does not trigger a change in reduction factors, and taxing authorities receive new revenue as new property is added. Likewise, reduction factors do not stabilize revenue when property is removed from a class through exemption, abatement, demolition, or reclassification. Also, reduction factors are not applied to un-voted millage within the 10 mill constitutional limit or to millage authorized by municipal charter.