I can confirm that there is a death for George McWilliams, a farmer, at Corick on 6th Oct 1878, aged 87, so born around 1791. His wife was still alive, and the informant was his son John who also lived in Corick:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1878/020492/7191006.pdf
George’s wife Roseanna died 10.1.1887 aged 85. Their son John was the informant. John himself died 2.3.1890 aged 60. His wife, Mary Orr, was still alive. That couple married 20.5.1887. John was a widower, Mary a spinster.
This is the family in 1901:
http://www.census.nationalarchives.ie/pages/1901/Tyrone/Clogher/Corick/1726058/
Daughter Margaret (Maggie) was born 7.9.1889 at Corrick. There was also a daughter Eliza born 20.3.1888 also at Corick.
Mary died 16.6.1906 aged 58. Her father Robert Orr of Tullybroom was the informant.
Probate abstract taken from the PRONI wills site:
Probate of the Will of John M'Williams late of Corick County Tyrone Farmer who died 2 March 1890 granted at Armagh to Thomas Mills of Ballymagown in said County Farmer.
The will itself is on-line on the PRONI site:
https://www.nidirect.gov.uk/services/search-will-calendars
It mentions his wife Mary and 2 daughters Margaret and Eliza. I don’t know where Eliza was in the 1901 census. However there is a tree on Ancestry (Ashley tree) which records her giving birth to children in British Columbia from 1913 onwards. So evidently she had moved to Canada by that year. She died in Kelowna, BC, on 12th May 1986, according to the tree. The tree gives no information on daughter Margaret. I don’t know what happened to her after 1901.
Administration of the Estate of Mary McWilliams late of Carrick County Tyrone Widow who died 16 June 1906 granted at Armagh to William Stockdale Auctioneer (Limited).
This is the Orr family in 1911:
http://www.census.nationalarchives.ie/pages/1911/Tyrone/Cloghan/Tullybroom/855956/
George McWilliams farm is listed in Griffiths Valuation for 1860. He had plot 5 which comprised a house, and just under 13 acres of land. He rented the farm from Rev John Story (who was the landlord for all the land in the townland).
If you were looking for the farm today it is on the Corick Rd, not far from the Corick House hotel which, in the 1800s, was where the Rev Story lived.
https://www.corickcountryhouse.com
You can see where the farm is/was by using the maps on the Griffiths website:
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearch
Birth and death registration only started in Ireland in 1864. Protestant marriages were registered from 1845 onwards. So for events before those years you need to consult church records. The McWilliams family was Church of Ireland. They are likely to have attended Clogher Cathedral. Its records go back to 1763. I don’t think they are on-line anywhere but there is a copy in PRONI (the public record office) in Belfast. A personal visit is required to view them.
George McWilliams was recorded as farming in Corick in the tithe applotment records in 1829:
https://cotyroneireland.com/tithe/clogher.html
George was married twice (at least). His first marriage appears to have been around 1830 or earlier as son John was born then. You would need to search the church records in PRONI to find it.
You say family history is that George McWilliams was born in Scotland. There’s no quick way of finding out exactly where he was born but my hunch is that he was born in Tyrone. A search of the church records might resolve that for you. Tyrone was heavily settled by Scots in the 1600s. (Something in excess of 100,000 Scots moved to Ireland at that time as part of the Plantation of Ulster and for other reasons such as famine in Scotland in the 1690s). That was the main settlement of Scots in the Tyrone area, though it’s not to say that George couldn’t have arrived after that. He was evidently there by 1829 anyway, and sufficiently well off to have acquired a farm. I don’t see any McWilliams listed in the Clogher area in the 1630 Muster Rolls so I’d say the family arrived after 1630.
This website says the name McWilliams is originally of Norman origins. The fact that your family were Church of Ireland and lived in Tyrone does tend to point towards them being settlers who arrived sometime from the 1600s onwards.
https://www.johngrenham.com/findasurname.php?surname=McWilliams
PRONI holds a document T2854/2 which describes life in the Corick area (and which might mention the McWilliams farm). The description in the PRONI catalogue is:
Typescript "The Economics of Country Life in Co Tyrone at the end of the 18th Century from Contemporary Records". This covers a 20/21 year period from 1790 and has been compiled from records kept by the Reverend Dr Story of Corick near Clogher.
