From the Wikipedia page 
Cornwall Record Office (CRO), part of Cornwall Council, is situated at Old County Hall in Truro and is the main repository for the historical archives of Cornwall.
Cornwall County Council was persuaded by Kenneth Hamilton Jenkin and others to set up Cornwall Record Office in the 1950s. Today its three and a half miles of shelving holds millions of individual historical documents, including deeds, leases, manorial records, parish registers, correspondence and diaries, maps and plans, council records and photographs; many of these relating to mining, fishing, farming and most other aspects of life in Cornwall. The documents range in date from the mid-12th century right up to the 21st century and they comprise an exceptionally valuable resource for local historians, family historians, ecclesiastical historians, mining historians and those undertaking research or academic projects.
Their online catalogue contains over a quarter of a million entries and is growing apace.
The website is 
The Wikipedia page on Cornwall is