« Reply #1 on: Tuesday 30 September 08 11:17 BST (UK) »
Don't know if this is new to you. The father of Richard, also called Richard, was the rector of Roche. There is a possible burial for father Richard aged 70 in St Austell 9/2/1829.
The only occurrences of the surname on the IGI in Cornwall are the baptisms of Richard and his siblings in batch C022211. It's certainly not a Cornish name, but from further north. Searching for Richard Postlethwaite on the National Archives gives results mainly in Cumbria and a few in Lancashire.
I can see Louisa's baptism in Topsham in Devon in 1832, but her marriage doesn't seem to be on the IGI. I've tried searching for Louisa born Topsham on various census years after her marriage, but nothing looks very likely - no children called after parents or relatives staying. Although there is a Louisa married to a shipwright William Blake and there is a William Blake on the same page as Louisa in the marriage index. You could buy her marriage certificate to be sure
Louisa Benedicta Selina Calideness Postlethwaite march qtr 1851 Exeter vol 10 pg 161
No sign of Richard in any later census either that I can see.
Cornwall: Allen, Bevan, Bosisto, Carnpezzack, Donithorn, Huddy, James, Retallack, Russell, Vincent, Yeoman
Cards: Thomas (Llanbadarn Fawr)
Glam: Bowler, Cram, Galloway, James, Thomas, Watkins
Lincs: Coupland, Cram
Mon: Cram, Gwyn, John, Philpot, Smart, Watkins
Pembs: Edwards (St. Dogmael's)
Yorks: Airey, Bowler, Elliott, Hare, Hewitt, Kellett, Kemp, Stephenson, Tebb