This county, together with a small part of that of Antrim, was anciently known by the name of Ulagh or Ullagh, in Latin Ulidia (said by some to be derived from a Norwegian of that name who flourished here long before the Christian era), which was finally extended to the whole province of Ulster. Ptolemy, the geographer, mentions the Voluntii or Uluntii as inhabiting this region; and the name, by some etymologists, is traced from them. At what period this tribe settled in Ireland is unknown: the name is not found in any other author who treats of the country, whence it may be inferred that the colony was soon incorporated with the natives, the principal families of whom were the O'Nials, the Mac Gennises, the Macartanes, the Slut-Kellys, and the Mac Gilmores. The county continued chiefly in the possession of the same families at the period of the settlement of the North of Ireland in the reign of King James, at the commencement of the seventeenth century, with the addition of the English families of Savage and White, the former of which settled in the peninsula of the Ardes, on the eastern side of Strangford Lough, and the latter in the barony of Dufferin, on the western side of the same gulf. It is not clearly ascertained at what precise period the county was made shire ground. The common opinion is that this arrangement, together with its division into baronies, occurred in the early part of the reign of Elizabeth. But from the ancient records of the country it appears that, previously to the 20th of Edw. II., here were two counties distinguished by the names of Down and Newtown. The barony of Ardes was also a separate jurisdiction, having sheriffs of its own at the same date; and the barony of Lecale was considered to be within the English pale from its first subjugation by that people; its communication with the metropolis being maintained chiefly by sea, as the Irish were in possession of the mountain passes between it and Louth. That the consolidation of these separate jurisdictions into one county took place previously to the settlement of Ulster by Sir John Perrott, during his government, which commenced in 1584, is evident from this settlement comprehending seven counties only, omitting those of Down and Antrim because they had previously been subjected to the English law.
The first settlement of the English in this part of Ulster took place in 1177, when John de Courcy, one of the British adventurers who accompanied Strongbow, marched from Dublin with 22 men-at-arms and 300 soldiers, and arrived at Downpatrick in four days without meeting an enemy. But when there he was immediately besieged by Dunleve, the toparch of the country, aided by several of the neighbouring chieftains, at the head of 10,000 men. De Courcy, however did not suffer himself to be blockaded, but sallied out at the head of his little troop, and routed the besiegers. Another army of the Ulidians having been soon after defeated with much slaughter in a great battle, he became undisputed master of the part of the county in the vicinity of Downpatrick, which town he made his chief residence, and founded several religious establishments in its neighbourhood. In 1200, Roderic Mac Dunleve, toparch of the country, was treacherously killed by De Courcy's servants, who were banished for the act by his order; but in 1208 he himself was seized, while doing penance unarmed in the burial-ground of the cathedral of Down, by order of De Lacy, the chief governor of Ireland, and was sent prisoner to King John in England. The territory then came into the possession of the family of De Lacy, by an heiress of which, about the middle of the same century, it was conveyed in marriage to Walter de Burgo. In 1315, Edward Bruce having landed in the northern part of Ulster, to assert his claim to the throne of Ireland, this part of the province suffered severely in consequence of the military movements attending his progress southwards and his return. Some years after, William de Burgo, the representative of that powerful family, having been killed by his own servants at Carrickfergus, leaving an only daughter, the title and possessions were again transferred by marriage to Roger Mortimer, Earl of March, through whom they finally became vested in the kings of England.
Transcribed from A Topographical Dictionary of Ireland, 1840 by Samuel Lewis