The History of Cornwall from the Cornwall Heritage Trust. I've got to say they don't do a bad job of recounting Cornish history but why not use the adjective 'Cornish' in the title? The word exists so why not make use of it? After all calling heritage 'English' doesn't seem to pose a problem.
They write: Cornwall’s prehistory and history help us to understand Cornwall today. The Duchy’s story is different from the rest of Britain: more survives here from the Neolithic and Bronze ages than in any other part of mainland Britain; the Romans made little impact on Cornwall; the middle ages saw Cornwall struggling to come to terms with being seen as part of “England”; and, to a huge extent, Cornwall can be seen as being as much a cradle of the industrial revolution as any other part of the country.