Few Cornish people are probably aware how wide-spread still with us is the belief in charms and charmers, ghosts, and all other superstitions; nor that there are witches in our county, shunned and dreaded by some who fear their supposed power to ill-wish those who offend them, and sought out by others who want by their aid to avert the evil eye, or by their incantations to remove the spells already cast on them and their cattle by an ill-wisher who has "overlooked" them. Folklore is an almost inexhaustible subject. There must be many charms in use here that have not come under my notice; a few are too coarse to record, as are some of the tales.
Margaret Ann Courtney's Cornish Feast and Folk-lore, first published in 1890, is a gathering of Cornish traditions, beliefs, and practices. The book is thematically arranged, covering seasonal festivals and divination customs, witchcraft, charms, and local legends. Each chapter testifies to an intimate engagement with the everyday beliefs and practices of rural Cornwall, and offers fascinating insight into how folklore supported both the sacred and the profane in 19th-century Cornish life. Particular stress is laid on regional variation within the county. Courtney's writing is also characterized by objectivity; she approaches folklore neither as quaint curiosities nor as primitive survivals, but as serious cultural artefact and therefore respects it.
Margaret Ann Courtney herself was a Cornish antiquarian and folklorist from Penzance. Coming from a well-known local family, she participated fully in the cultural life of her home town and county. Besides Cornish Folklore, she co-authored Glossary of Words in Use in Cornwall, contributing significantly to the documentation of regional dialects and word usages.
This is kind of disorganized, but a useful source if you want specific Cornish nineteenth-century stories. There are several towns I'm surprised weren't really mentioned — Truro chief among them — but the ballads are nice and I'm glad I know this exists.