Ancient Times

Ireland may have been one of the last parts of Europe to be occupied by man. Man has probably inhabited Ireland for less than 10,000 years, very low compared to the millions of years of inhabitation in other parts of Europe. It is thought the glaciers of the northern part of Europe had something to do with this lack of settlement.
These glaciers changed the nature of the landscapes that they covered. In Ireland, for example, they removed most of a several hundred feet thick layer of chalk that had covered much of the island. During the last cold stage that began at least 70,000 years ago, animals such as mammoth, hyena and reindeer roamed the cold tundra steppes in Ireland before ice sheets eventually accumulated over most of the island.
The following ancient territories, were in existence from prehistoric times to the break-up the Gaelic order in the sixteenth century:
" Breffny (Breifne): Cavan and west Leitrim.
" Corca Laoidhe: Southwest Cork.
" Dalriada: North Antrim.
" Decies (Déise): West Waterford.
" Desmond (Deasmhumhan): Kerry and much of Co. Cork.
" Iar Connacht: West Connacht, mainly Connemara.
" Muskerry (Muscraidhe) Northwest and central Cork.
" Oriel (Orghialla): Cos. Armagh and Monaghan and parts of south Down, Louth and Fermanagh.
" Ormond (Urmhumhan): Much of Co. Kilkenny and north Tipperary.
" Ossory: The extent of the ancient kingdom of Osraighe was approximately the same as that of the diocese of Ossory, ie. Co. Kilkenny and some adjacent areas.
" Thomond (Tuathmhumhan): Most of Co. Clare with adjacent parts of Cos. Limerick and Tipperary.
" Tirconnell (Tir Chonaill): Co. Donegal.
" Tirowen (Tir Eoghain): Co. Tyrone with adjacent part of Co. Derry.