The ancient province of Laigin derives its name from the Laigain people who were among the earlier inhabitants of the area. The Laigin, modern spelling Laighin were a population group of early Ireland. They gave their name to the province of LeinsterIncluded among the early peoples were the Cauci, Manapii, Coriondi, Brigantes, Domninii and Usdiae. By the 5th century the Southern Ui Naill encroached on the Northern borders of the province decreasing its area. The Ui Chennselaig and Ui Dunlainge tribes were the dominent septs during this period. Others included the Ui Faelain, Cuala, Ui Garrchon, Ui Drona, Ui Biarrche and Ui Enachglais, with the sacred capital at Naas.
As its borders expanded in later centuries the territories of the Fine Gall (Dublin), Ui Dunchada, Ui Failge, Loiges, Osraige, Eile, Fothairt, Ui Mail and Ui Muiredaig were included. Later the more prominent clans included the MacMurroughs, O’Tooles, Phelans, O’Connors, Kilpatricks, O’Byrnes, O’Moores and O’Dempseys.
The arrival of the Anglo-Normans occured in Leinster in 1169/70, at the invitation of the ousted King of Leinster, Dermat MacMurrough. Earldoms were established in Kildare (Fitzgeralds) and Ormond (Butlers). The area of English control around Dublin, referred to as the Pale, expanded into the province of Leinster next with settlements and fortifications by the new Anglo-Normans lords. By the 17th century, the Cromwellian campaigns supplanted these with English rule and land ownership.