McMillan chose the Buckeyes over Alabama, Clemson and Auburn.
The 6-foot-2, 249-pound Under Armour All-American gives a huge recruiting win to Urban Meyer, who continues to recruit the Southeast extremely well. McMillan will join quarterback Stephen Collier (Leesburg, Ga./Lee County High) with the Buckeyes.
In the 2013 class, Ohio State signed inside linebacker Trey Johnson (Lawrenceville, Ga./Central Gwinnett) and safety Vonn Bell (Rossville, Ga./Ridgeland) from Georgia, along with defensive end Joey Bosa (Fort Lauderdale, Fla./Saint Thomas Aquinas) and wide receiver James Clark (New Smyrna Beach, Fla./New Smyrna Beach) out of Florida.
Ohio State has eight ESPN 300 commits, including one of the top linebacker classes in the nation with McMillan, No. 7 outside linebacker Dante Booker Jr. (Akron, Ohio/St. Vincent-St. Mary), No. 22 outside linebacker Kyle Berger (Cleveland/Saint Ignatius) and No. 40 outside linebacker Sam Hubbard (Cincinnati/Moeller).
The Buckeyes remain in the hunt for a number of other prospects, including No. 31 Solomon Thomas (Coppell, Texas/Coppell), No. 39 Johnnie Dixon (Palm Beach Lakes, Fla./Dwyer), No. 50 Marshon Lattimore (Cleveland/Glenville), No. 68 Malik McDowell (Southfield, Mich./Southfield) and No. 228 Erick Smith (Cleveland/Glenville) among others.
McMillan will graduate this month and enroll at Ohio State in January.