The O Duigenans of Castlefore were descended from Pilib na hInnse, Philip of the Island, a brother of Ferghal Muimhneach previously mentioned. They seem to have settled in this place ca 1400. Maghnus O Duigenan of Castlefore, in conjunction with Solmon O Droma and R. McSteighe, compiled the Book of Ballymote (in the castle of Ballymote) about 1391, for McDonough Lord of Coran. The McDonoughs sold it in 1522 for one hundred and forty milch cows to Hugh ODonnell
of Tirconnell; it is written in early medieval Irish style. A copy of this book can be seen in the museum at Rosnowlagh, Donegal. Magnus O Duigenan was by far the chief subscriber. It is the first and best known manuscript of the O Duigenan's compilation;it is a compendium of medieval lore, legend, history, genealogy, topography, etc.Magnus O Duigenan was third in descent from Philip, died in1452, and is described as "O Duigenan of Castlefore". The name Philip was common among the O Duigenans.

The O Duigenan family were associated with several of the Annals, which are the most reliable source of Irish history for 1000 years down to the 16th century. The records for the early periods were taken from older manuscripts now lost. Members of the O Duigenan family assisted in the
compilation of the following Annals:

(1) The Annals of Loch Ce-dealing mainly with events in Connaught from 1014-1571.

(2) The Book of the O Duigenans of Kilronan-to which the Four Masters acknowledged their debt.

(3) The Annals of the Four Masters-one of whom was Peregrine O Duigenan of Castlefore.

(4) The Book of Ballymote-one of the seven great books of Ireland, compiled in 1391 by Marcus O Duigenan for Brian MacDonagh of Corran.

Of course the best known of the books of Irish history with which they are associated is The Annals of the Four masters, through the contributions of the scribe Pergrine O Duigenan.