Parish registers online
1.2 million Cornwall baptisms and marriages are included in the IGI at FamilySearch but not all parishes are included (you can see the coverage here).
There are over half a million transcribed baptisms, marriages, burials, and memorial inscriptions at Findmypast, and a much smaller number at Ancestry.
The volunteers of FreeREG have transcribed over 358,000 baptisms, 185,000 marriages, and 163,000 burials for Cornish parishes.
However, by far the best source for parish register entries is the Cornwall Online Parish Clerks site where there are approximately 2.4 million parish entries transcribed. The coverage by parish is shown here (also check out the OPC site for other smaller databases).
Births, marriages and deaths
Registration districts in Cornwall
There are no local BMD indexes for Cornwall
Pre-1841 censuses
Boyton 1821, Poundstock 1811, St Breock 1824, St Endellion 1833/34, St Hilary 1801, St Just in Pwenwith 1588-96, Veryan 1821
Also consider....
Reproduced courtesy of Francis Frith.
Key Cornwall resources
Cornwall Record Office in Truro holds parish registers for the whole of Cornwall; other key records include records of the Quarter Sessions and Petty Sessions, and about 80,000 pre-1858 wills and similar documents relating to the Archdeaconry of Cornwall and the Deanery of St Bunyan (note that some of the wills for other parts of Cornwall were lost when the Exeter Probate Registry was completely destroyed in 1942). A CARN pass is required if you visit, but one can be issued on arrival provided you have appropriate identification. If you are unable to visit in person there is a paid research service which costs £29 per hour.
The Cornish Studies Library in Redruth holds tens of thousands of printed works relating to Cornwall, over 30 local newspapers on microfilm, a large collection of maps, and over 160,000 photographs and postcards from the mid-19th century onwards.
Cornwall Family History Society is based in Truro, and offers a paid research service (£10 per hour for non-members).