Hi Philip, I think the William Corkill mentioned in this thread is the brother of my ancestor Esther Corkhill or Corkill b. 1807 Kirk maughold
I have a copy of her marriage certificate to Joseph Saywood in Hornsey Nth London 1838, which gives her father as William Corkhill a Farmer. I also have a copy of a hand written saywood family tree with Esthers parents given as William Corkill 1765-1836 born Balnagory or ballajorch nr Ramsey & Esther McNeil or McNeill 1765/75-1820 (ties up with early 1821 burial) born Barra Outer Hebredes.
I have also found a marriage in Lezayre between William Corkill & Esther Kneale (Manx version of McNeil I believe) in 1791 & several children baptised in Maughold. Not sure how these message boards work but I would be pleased to hear from you.
Jim