William Corkill's age in census's 1851-1881 is 44, 54, 64, 74, which points to about 1806-07.
Worth pursuing might be an IGI bapt of William Corkill s/o William Corkill and Isabella Kerney 8 Mar 1806 Lezayre.
A sister might be Margaret Kewney d/o William Corkill & Isabella Kewney 30 Oct 1803 Lezayre.
Marriage William Corkill & Isabella Kewney 28 Jul 1805 Lezayre.