Cornwall by Sabine Baring-Gould — Read

Before the Conquest the divisions of the county were probably those afterwards forming the old deaneries, and followed the limits of the Celtic tribes under their several chiefs. Of these there were eight: -- East and West, Kerrier, Penwith, Powder, Pyder, Trigg Major, and Trigg Minor, but at the Conquest a redistribution was made in hundreds. These were Conarton, Fawiton, Pawton, Riatton, Stratton, Tibesta or Tibesterna, and Winneton. There may have been an Anglo-Saxon redistribution. But it was a rearrangement that did not last, and never commended itself to the people, and it is not easy now to ascertain what the limits were. Conarton was Penwith. Perhaps Tibesta was Powder and Winneton Kerrier. East and West composed one district of Wyvelshire.

Cornwall was first an Earldom, and then accordingly a County, but when raised to be a Dukedom it became a Duchy. It had two chief officers, the Earl and the Sheriff, the latter appointed by the crown.