Hi Noreen,
Thank you for your message.
Have you tried looking for Cornelius in the land records pertaining to Ireland in the 19th century? Although these do not offer any genealogical information they can sometimes be used to toe a person to a specific place. Once you have a specific place more avenues of research will open up to you. There are two:
The Tithe Applotment Books (1823-1838) found at http://titheapplotmentbooks.nationalarchives.ie/search/tab/home.jsp
and Griffith?s Valuation (1848-1864) found at http://www.askaboutireland.ie/griffith-valuation/
Also, if the Castleisland that you are referring to is the civil parish in CO. Kerry you may be in luck. Irish Genealogy have begun to upload church records to their websites free of charge. It is an ongoing project so only about 4 counties have been covered so far, one of which is Kerry. So if Timothy was from Kerry you may be able to find his birth record here:
http://churchrecords.irishgenealogy.ie/churchrecords/
I hope this is helpful.
Kind regards,
Genealogy Support