Griffiths Valuation lists Isaac Whitfield farming in Killatee in 1857. In the 1901 census there’s John, who is his son:http://www.census.nationalarchives.ie/pages/1901/Cavan/Coron...
John was originally from Tyrone and his wife from Armagh. The family were Quakers which may help you as Quakers kept excellent genealogical records.
The 1911 census tells us the couple had had 5 children, of whom 2 were still alive.http://www.census.nationalarchives.ie/pages/1911/Cavan/Corra...
John Whitfield married Sarah Jane Allen on 1st Feb 1866 in Richhill Meeting House, Co Armagh. He was a widower and his father was Isaac, a farmer. (So Rebecca was evidently his mother). John’s address was Killatee. Sarah Jane’s was Causanagh, Co. Armagh.https://civilrecords.irishgenealogy.ie/churchrecords/images/...
There’s a copy of the Richhill Quaker records in PRONI in Belfast.
John Whitfield died 24.3.1923 at Killatee. Sarah Jane had pre-deceased him on 13.9.1919. His son John, also of Killatee, was the informant.
John Whitfield (junior) died 14 Nov 1945 at Killatee. The informant appears to be Elaine Risque (the writing is not clear), sister in law, also of Killatee. John’s wife was still alive in 1945. John left a will which should be in the National Archives in Dublin. That may give you details of any descendants. Probate was granted in Dublin on 21.5.1946 to his widow Mary H. Whitfield. John’s occupation was retired manager.
John Whitfield senior also left a will. Probate was granted 17.3.1923 at Cavan to John junior. Again that will should be in the National Archives in Dublin. They will copy it for you (for a fee).
This may be John junior in the 1901 & 1911 censuses. He married twice. (First wife was Sarah Jane McFadden. Married 17.6.1891 at Cootehill Meeting House). Second wife was May Harvey Scott. Married 10.9.1896 at Belfast Friends Meeting House. They had no children (by 1911 anyway).http://www.census.nationalarchives.ie/pages/1901/Down/Victor...http://www.census.nationalarchives.ie/pages/1911/Antrim/Clif...
May Harvey Whitfield seems likely to be the Mary H. Whitfield who got probate in 1946.
May Whitfield death looks to be on 16.4.1965 in Belfast aged 88. (You can view that certificate on the GRONI website).
Whitfield, Mary Harvey of 56 Castlereagh Road Belfast widow died 16 April 1965 Administration W/A Belfast 22 June to David Chambers clerk. Effects £484 5s.
The probate file should be in PRONI (the public record office) in Belfast.
There are no Whitfields listed in Co. Cavan in the current phone book.
No Allens in Causanagh in the 1901 census.