His son, Sir Neill O'Neill fought for James II.
The descendants of Niall spread over Ireland and became divided into two main branches, the northern and the southern Hy Neill, to one or other of which nearly all the high-kings (ard-ri) of Ireland from the 5th to the 12th century belonged; the descendants of Eoghan being the chief of the northern Hy Neill.'
Neill Mor's great-greatgrandson, Henry O'Neill, was created baronet of Killeleagh in 1666.
Through an elder line from Neill Mor was descended Brian Mac Phelim O'Neill, who was treacherously seized in 1573 by the earl of Essex, whom he was hospitably entertaining, and executed together with his wife and brother, some two hundred of his clan being at the same time massacred by the orders of Essex.
The subsequent history of Benares contains two important events, the rebellion of Chait Singh in 1781, occasioned by the demands of Warren Hastings for money and troops to carry on the Mahratta War, and the Mutiny of 1857, when the energy and coolness of the European officials, chiefly of General Neill, carried the district successfully through the storm.