Ohio Rev. Code § 135.17: Cash reserve.

Each treasurer may at all times keep in the vaults of his office such amount, as a cash reserve, as is prescribed by the proper governing board, which amount shall not be required to be deposited pursuant to sections 135.01 to 135.21, inclusive, of the Revised Code. Each treasurer shall deposit or invest all the remaining public moneys in his possession in accordance with sections 135.01 to 135.21, inclusive, of the Revised Code.