Fir Rois - Feara Rois, or Fer Rois, was located in south Airghialla. Locations for Fir Roiss are cited in Onomasticon Goedelicum in the barony of Farney, co. Monaghan, and in the barony of of Ardee, co. Louth, and in Meath. Crích Ross stands 4 miles northewet of the point where counites Monaghan, Louth and Meath meet. An O'Finn sept is noted here as chiefs prior to the coming of the Anglo-Normans. O'Dugan (Poems) mentions O'Cosgraigh as king of smooth Feara-Rois. Mael Ruiss or Mael Roiss are the same as Mael Rubha, meaning servant or lad of Ruba or Ros, next in importance to Column Cille of the Scottish-Irish Church to Dalriada.

An early genealogy of the Fir Rois: Gairbith m. Maileidig m. Feradaich mc. Finain m. Failbi m. Duibthaich m. Crundmail m. Fathaich m. Faelbi m. Lugdach mc. Fiacrach Cenn Findain (a quo hI Ceind Find) m. Feidlimid.

Located in western Co. Cavan and northern Co. Meath. The Mugdorna occupied this territory prior to 800 AD, when they were pushed out of Meath and into Monaghan and replaced by the Gailenga. The Gailenga Mora left their name in the barony of Morgallion (Machaire Gailenga, "the plain of the Gailenga") in County Meath. The O'Lohan or O'Loughan (Ui Leochaín) sept were lords of the Gailenga Mor before being driven across the Shannon after the arrival of the Normans. The Ua hAonghusa (O'Hennessy) sept of Gailenga Becc was located on the Co. Dublin/Meath border. The Gaileanga have an early genealogy tradition back to Ailella Auluimm (Oilill Olum).

The Mughdhorna apparently also occupied a part of what is now county Louth. In the twelfth century . . . the political center of gravity of this whole region moved to Louth as the O'Carroll lords pushed southwards. That tendency continued under the Normans and while Farney remained in the diocese of Clogher, most of its churches were linked with those of county Louth, mainly Louth itself and Ardee. It is important to note that the deanery included not only the present barony of Farney but that of Cremorne as well. That reminds us that the Mugdorna people, who gave us our earliest references to the Maighean, (a word which means precinct), predate Fir Farney in this region.

Donaghmoyne (Domhnach Maighean), as a parish, was alternatively known as Clann Cearbhaill after the O'Carrolls, or Farney, after the Barony [which was earlier known as the barony of Donaghmoyne]

Ros Cluain is an intriguing amalgam of the names of the present Machaire Rois and Magheracloone. It may be that together they formed one parish at the time of the list [of parishes compiled in the early years of the 14th century]. Ros as a church name can be traced back to the seventh century. In Adamnan's life of St Colmcille there is a reference of 'Cell Rois in provincia Maugdornorum'.

Over six centuries later, in the 13th century, Ros is still in the land of the Mugdorna, as indeed is Donaghmoyne. It is impossible to say exactly when the Mugdorna territory shrank to the area of the present barony of Cremorne which preserves their name. But it seems certain that Ros, or Machaire Rois, at least originally, was distinct from the Fir Rois, a tribe associated with the barony of Ardee in Co Louth. The first mention of Machaire Rois occurs in 1541 when the parish is called St Finian's of Ros alias Machaire Ros.