New Settlers in Mayo and Sligo
In the 12th century John de Courcy made some attempts with his Anglo-Norman forces towards the conquest of Connaught, but did not succeed to any extent. The De Burgos or Bourkes, in the reign of King John, obtained grants in various parts of Connaught; and, for a long period, carried on fierce contests with the O'Connors, kings of Connaught, and various chiefs. They made considerable conquests in the country, and were styled lords of Connaught; but it appears that in the fourteenth century, several chiefs of the Bourkes renounced their allegiance to the English Government, and some of them took the sirname of "MacWilliam;" and, adopting the Irish language and dress, identified themselves with the ancient Irish in customs and manners. One of them took the name of Mac William Oughter or Mac William the Upper, who was located in Galway, the upper part of Connaught; and another, Mac William Eighter, or Mac William the Lower, who was located in Mayo, or the lower part. Some branches of the Bourkes took the sirnames of MacDavid, MacPhilbin, MacGibbon, from their respective ancestors. (See the "Bourke" pedigree.)
From Richard or Rickard de Burgo, a great portion of the county Galway got the name of Clanrickard, which, according to Ware, comprised the baronies of Clare, Dunkellin, Loughrea, Kiltartan, Athenry, and Leitrim. The De Burgos became the most powerful family in Connaught, and were its chief governors under the kings of England. They were styled lords of Connaught, and also became earls of Ulster; but, on the death of William de Burgo, earl of Ulster, in the fourteenth century, and the marriage of his daughter Elizabeth, to Lionel, Duke of Clarence, son of King Edward the Third, his titles passed into the Royal Family of England.
Ulick Burke, the progenitor of the marquises of Clanrickard, had great possessions in Galway and Roscommon; and Sir Edmund Bourke, called "Albanach," had large possessions in Mayo, and was ancestor of the earls of Mayo.
Mayo: The other families who settled in Mayo, were the following:—De Angulo or Nangle, who took the Irish surname "MacCostello," and from whom the barony of "Costello" derived its name. De Exter, who took the name of "MacJordan," and were styled lords of Athleathan, in the barony of Gallen. Barrett, some of whom took the sirname of "MacWatten;" and "MacAndrew." Staunton, in Carra—some of whom took the name of "MacAveely." Lawless, Cusack, Lynot, Prendergast, and Fitzmaurice; Bermingham, who changed their name to "MacFeorais;" Blake, Dillon, Bingham, etc. The MacPhilips are placed on the map of Ortelius in the barony of Costello; their principal seat is at Cloonmore, and they are a branch of the Bourkes who took the name of "MacPhilip."
Mayo, according to some accounts, was formed into a county, as early as the reign of Edward the Third; but not altogether reduced to English rule till the reign of Queen Elizabeth. In Speed's "Theatre of Great Britain," published, A.D. 1676, Mayo is stated to be "replenished both with pleasure and fertility, abundantly rich in cattle, deer, hawks, and plenty of honey." Mayo derives its name from "magh," a plain and "eo," a yew tree, signifying the Plain of the Yew Trees.
In Sligo, the Anglo-Normans under the Bourkes and the Fitzgeralds (earls of Kildare) made some settlements, and had frequent contests with the O'Connors; and with the O'Donnells (princes of Tirconnell), who had extended their power over a great part of Sligo. Sligo derives its name from the river Sligeach ("Slig," a shell), and was formed into a county, A.D. 1565, in the reign of Queen Elizabeth, by the lord deputy Sir Henry Sydney.