HI Alex and Jacqueline,
I am decended from Johnstons and Campbells on Islay and while I haven't been to Islay, I have been researching it on and off for 20 years and hooked up with some older researchers around 2000 who wrote fairly extensive messages on the Islay rootsweb pages. There was definitely a Toni Sinclair researching in that group.
In the 1840 census I have family living at Keils:
1841 Census
Mary Johnston and children were found living at Islay during the 1841 Scottish Census. Angus has not been found.
Parish No Place Name Surname Age Occupation Born
Kilmeny 227 6 Keills Mary Johnson 35 Ind. ARY
Kilmeny 227 6 Keills Mary Johnson 12 ARY
Kilmeny 227 6 Keills Janet Johnson 7 ARY
Kilmeny 227 6 Keills Angus Johnson 3 ARY
Kilmeny 227 6 Keills Alexander Johnson 2 ARY
Kilmeny 131 20 Ballygrant John Johnston 14 ARY
Not sure what they were doing there and most of them ended up in Glasgow by the 1850s.
I don't know if that helps.
Best wishes,
Rowena