Hi Ed, Welcome to Ireland Reaching Out,
Unfortunately because it happens to be so far back, the chances of finding a Birth, Marrage or Death Record for the Parents Patrick Shevlin and Agnes Breslin would be slim indeed. To be truthful searching for Donegal Records back in the early 1800’s is an extremely difficult task, because the records are simply not available back then throughout Co.Donegal. Church Records if you are lucky started approximately about 1830’s for Church of Ireland/Prepyterian Religion and later on again in the 1850’s for the Catholic Religion.
I would however recommend you taking out a short subscription to search the transcribed records within http://www.rootsireland.ie/ as they would have the best database and earliest Records available to research,There would be a chance you would find Records referencing Shevlin families in that area of Ardara close to the timeframe you are interested in. They might not seem immediate family at first, however you might find similarities that lean you towards them being closely related. Sometimes putting them all together within a family tree is a good way to visually see the families and it may just help you connect you to others that are researching these Shevlin families also.
There are a few other type of Donegal records available to search back in the early 1800’s.
The Tithe Applotment Books which was compiled in the 1820’s and 1830’s tell only the names of some of the tenants and farmers that happened to be able to afford the leasing of land at that time. The names within the Tithes Applotments are a generation before that of the follow on family names given in the 1858 Griffith Valuation which would be a more accurate Record. They tell the names of all head of home of all families just like the Holmes that were leasing or owning land back in the 1850’s.
I have had a good search of these for Shevlin families using ancestry.com, and I have attached a short list of all the Shevlin families and locations in Donegal,for the 1820’s Tithe Applotment Books and the 1850’s Griffith Valuation. There will be a few from the list that will grab your attention and you can follow on by checking them out on the National Archives - Tithe Applotment Book page, using Shovlin Search Shevlin Search , and also the askaboutireland site for the 1858 Griffith Valuation Page 1 Page 2 results.
There would be a few Shevlin Families showing withìn the general area of Ardara in the 1900’s also worth checking out.1901 Census ireland - Donegal - Inishkeel 1911 Census ireland - Donegal - Innishkeel
As regards the location "Ardara (Possibly Barkillew a hilltop townland near Maghera", you're directions were very good, and so I have attached a few links below that will take anyone interested directly to that townland - Ardara Townland, Co. Donegal. Ardara is in the Electoral Division of Ardara, in Civil Parish of Killybegs Lower, in the Barony of Banagh, in the County of Donegal.
I hope this is of some help to you. Because this message you posted is up here on the Irelandxo Site, it heightens the chance of someone local seeing it, or someone research Shevlin "googleing" it and getting in contact with you in the future. I wish you all the best with your research going forward.
Seamus Callaghan
