Hello Anne,
The large number mentioned by nenny4 weren't there at the time of the Valuation in Co. Donegal in 1857. The extracts show one in Tyrone and three in Donegal ... two of them are called William. There were no others in Ireland so I'd suggest concentrating the search in Donegal.
William Crumlish, Town Parks of Strabane, Camus, Tyrone
William Crumlish, Monclink, Raymoghy, Donegal
Daniel Crumlish, Gortnaskea, Fahan Upper, Donegal
John Crumlish, Drummay, All Saints, Donegal
Have you contacted Martin McMenamin who is searching for the
Crumlish family in Ireland on Genforum. His ancestors lived at Gortnaskea and Monreagh in the Parish of Upper Fahan, Inishowen Co. Donegal.
Chris