the name of two baronies of Ireland, in the county of Down, and province of Ulster. They are distinguished into Upper and Lower Ivecach, and the former is by much the largest barony in that country. The name of Ivecach, or Hy Veoach, is said to be taken from Achaus, in Irish called Eochach, grand-father to King Coaltbriga, as much as to say "the territory of Eochach;" for hy, in the Irish language, is a common adjective, denoting not only the heads and founders of families, but also the territories possessed by them. Ivecach (including both baronies) was otherwise called Magennis's country, and in Queen Elizabeth's time was governed by Sir Hugh Magennis, esteemed to have been one of the most polite of all the natives in those parts. Through part of this barony runs a chain of mountains considerably high, known by the name of Ivecach mountains.

IERNUS, in Ancient Geography, a town in the south-west of Ireland. Now Dunkerrow, (Camden); called Donegynne by the natives, situated on the river Maire, in the province of Munster.

IERNUS, or IERNUS (Ptolemy), a river in the southwest of Ireland. Now called the Maire, or Kenmare, running from east to west, in the province of Munster.