Cornwall by Sabine Baring-Gould — Read

The original population of Cornwall would seem to have been what is now commonly called Ivernian, the same as Iberian, the underlying race everywhere in Western Europe from the western isles of Scotland to Gibraltar. When the Romans invaded and conquered Spain, they found there already in the east the Celts and in the west the Iberians, and they designated the more or less fused population, Celtiberians. So in Cornwall, there was this dark-haired, dusky-skinned race, and the Brythons, Celts, of the people of the Dumnonii. There were extensive settlements by Irish in the Land's End district, the Lizard, and along the north coast, in 490-510, owing to the expulsion of the Ossorians and the Bairrche from their lands in Ireland. The Saxon also crossed the Tamar and peaceably settled in East Cornwall.

The language spoken was Brythonic, akin to, and originally identical with Welsh and that spoken in Lower Brittany. It was distinct in some points from the Goidelic of Ireland, the Isle of Man, and the Highlands of Scotland. The main difference was that the _C_ in the latter became _P_ in the former. Thus _Ken_ or _Cen_ in such names as Kenmare and Ciaran would in Cornish become Penmare and Piran.