The Laigainian colonization is believed to have taken place sometime about 300 B.C., and are believed to have come from the northwestern region of Gaul, later Normandy. They are mythologically referred to as the Tuatha De Danann. Their name association with "Laighi," the ancient name for Leinster, suggests that this was where they first settled The ancient province of Laigin derives its name from the Laigain people who were among the earlier inhabitants of the area. Included among the early peoples

• Cauci
• Manapii
• Coriondi
• Brigantes
• Domninii
• Usdiae

By the 5th century the Southern Uí 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. Eventually, they extended their power to Connacht, and in the process forced the Firbolg tribes into the remoter parts of the province. The remains of many great stone forts built by the Firbolgs in their defense against the Laigain tribes can still be seen in remote areas of western Ireland.

Within a few generations the Laigain tribes had established themselves in Connacht, where in County Sligo their descendants include the O'Haras, O'Garas, and others. The ancient Laigin or Dumnonii group moved from the western region of Normandy as the Roman built up pressure on Gaul about 100 B.C. The Laigin settled first in southern Britain and then in Ireland. The Uí Neachtain (Naughton) are said to belong to the Laigain group, later living in the territory of the Ui Maine. As its borders expanded in later centuries the territories of the

• Fine Gall (Dublin)
• Ui Dunchada
• Ui Failge
• Loiges
• Osraige
• Eile
• Fothaírt
• Ui Mail
• 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.