Ohio Rev. Code § 5736.12
The tax commissioner may prescribe requirements for the keeping of records and other pertinent documents, the filing of copies of federal income tax returns and determinations, and computations reconciling federal income tax returns with the returns and reports required by section 5736.04 of the Revised Code. The commissioner may require any person, by rule or notice served on that person, to keep those records that the commissioner considers necessary to show whether, and the extent to which, a person is subject to this chapter. Those records and other documents shall be open during business hours to the inspection of the commissioner, and shall be preserved for a period of four years unless the commissioner, in writing, consents to their destruction within that period, or by order requires that they be kept longer. If such records are normally kept by the person electronically, the person shall provide such records to the commissioner electronically at the commissioner's request.
R.C. § 5736.12