In IGI :-
William Corkill married Jenny Blake in Padstow 1771.
A William Corkill and a Jenny had the following children christened at St Nicholas Whitehaven:
Also at St Nicholas the following children were christened to William Corkill and a Jane:-
John Blake 1773
Merria ( Maria) 1783
The sequence of dates fit the same parents.
Back in Cornwall, John Blake Corkill married Melicent Avery in 1796 and a John Avery Corkill married Susan Nankwell in 1824.
The use of the mothers maiden name may be significant.
Could this add to your Whitehaven- Cornwall theory.