Hi Mirla
As has already been said there are three confirmed henges in the county, Castilly, Castlewich and the Stipple Stones. All three can be found on this website. I am also putting forward my 'henge' on Bodmin Moor until anyone tells me otherwise!
http://www.themodernantiquarian.com/site/6760/letter_moor.html
I have not visited Castilly or Castlewich but the Stipple Stones is a great site..but not that easy to get to..
I have not yet had a look at Tye farm and St Newlyn is a new one to me..
Mr H