I see only one reference to the place name in Ireland, the reference in the Raphoe Wills, I take it this is the reference to which you are referring, have you any other details about these Tonners? Where were they found in latter generations, may be able to narrow search down, it may be the subdivision of a townland, or a mispelling there is a Creaghadoos townland in the Parish of Taughboyne which falls within the Raphoe Barony
There is or was a Creachdow in Argyll, Scotland, put a google search in for Creachdow, Scotland brings up a few results but they are from the 16/17C
Joe