OH Const., Article XII, Section 7

Laws may be passed providing for the taxation of the right to receive, or to succeed to, estates, and such taxation may be uniform or it may be so graduated as to tax at a higher rate the right to receive, or to succeed to, estates of larger value than to estates of smaller value. Such tax may also be levied at different rates upon collateral and direct inheritances, and a portion of each estate not exceeding twenty thousand dollars may be exempt from such taxation. (Adopted Sept. 3, 1912.)