Ohio Revised Code Title LVII. Taxation § 5731.10

(A) The value of the gross estate shall include the value of all property, to the extent of the interest therein held by the decedent and any person jointly, so that upon the death of one of them, the survivor has or the survivors have a right to the immediate ownership or possession or enjoyment of the whole property, except such part thereof as may be shown to have originally belonged to such other person or persons and never to have been received or acquired by the latter from the decedent for less than an adequate and full consideration in money or money's worth.

(B) When the person [sic] holding property jointly are a husband and wife, the amount includible in the gross estate shall be one-half the value of said property. When the property has been acquired by gift, bequest, devise, or inheritance by the decedent and any other person or persons as joint owners and their interests are not otherwise specified or fixed by law, the amount includible in the gross estate shall be the value of a fractional part of said property determined by dividing the value of the property by the number of joint owners.