Bellanacargy castle, anciently referred to as Ballynacarraig because it was built on a carraig (rock island) situated in the middle of the Annalee river, was destroyed in May 1689 by Williamite forces led by Thomas Lloyd.

During the Parliamentary session of 1640 he was enlisted by Rory (Roger) O'Moore in the plot to start a rebellion against English rule in Ireland.

He raised a brigade of twelve hundred men, composed chiefly of his name and family, and served with distinction as lieutenant-general in the service of the Confederate Catholics of Ireland.

In his diary for 3 June 1644, Sir James Ware (historian) states "Intelligence came to Dublin that Roger Moore and Philip O'Reilly, two of the first incendiaries were committed to prison at Kilkenny".

Eibhlin, who married Colla Dubh Mac Mahon, and whose son was Most Reverend Hugh MacMahon, Roman Catholic Archbishop of Armagh; 3.

John Colgan, the eminent Donegal hagiographer, dedicated his treatise on Duns Scotus, published at Antwerp in 1655, to Philip O'Reilly.