The O'Neill Clandeboy (Ó Néill Clann Aodha Buidhe) who reigned in the territory descended from Hugh Boy O'Neill, a king of Tyrone. His descendants took advantage of the demise of the Earldom of Ulster during the latter 14th century and seized vast portions of territory. Clandeboye's main seats of power were Shane's Castle and Castle Reagh.
The kingdom came to an end at the dawn of the 17th century after Con O'Neill, the last head of the Clandeboye O'Neill’s of Upper Clandeboye, signed away two-thirds of his land to his close associates Hugh Montgomery and James Hamilton who proceeded to privately settle their land with settlers from Great Britain just prior to the larger Plantation of Ulster. Con died in 1618. James Hamilton became the first Viscount Claneboye in 1622.