Ohio Rev. Code § 135.40: County cash reserve.

A county treasurer may keep at all times in the vaults of his office such amount of public moneys, as a cash reserve, as he deems to be necessary to transact the business of his office, which amount shall not be required to be deposited in public depositories. All the remaining public moneys in his possession shall be deposited in public depositories in accordance with sections 135.31 to 135.40 of the Revised Code.