The first name David was borrowed from the Hebrew Old Testament. In Old French the vernacular form was Davy and this entered Middle English with the Norman invasion of 1066. The name David was popular earlier than that in Wales (where the cult of St David was centred) and Brittany. Therefore, we might presume that this was also the case in Cornwall, although the direct evidence is lacking.
Be that as it may, Davy was obviously a common name in the Cornwall of the early 1500s. It was found almost everywhere, while the 1641 distribution reveals particular concentrations in parts of south-east Cornwall. By then seven per cent of Davys had acquired an -s. A hundred years later in the mid-18th century that proportion was over a third.
However, the growing proportion of the spellings Davies and Davis then halted and fell back. In 1861 28 per cent of the 536 Davy etc. households were Davies/Davis, while the vast majority had settled for the spelling Davey. By then, the greatest number of Davy/Davies households could be found in the Camborne-Truro-Falmouth triangle.
Cornish studies resources 