I am the only son of Brendan Concannon, who was in turn the younger son of Thomas Concannon of Galway (d. 1958) who was the eldest son of Malachy and Delia Concannon.
Thomas had a number of siblings including a Mary (known as Mamie)and two other sisters Delia and (I think) Maureen, who were nuns in the Oranmore convent, both of whom survived well into the 1960's. He also had at least three brothers, Austin (who farmed in Tierbuoy Co. Galway), Malachy (a priest who served East Grinstead in Sussex for forty years or so) and Willie, who was a solicitor in Tuam for many years. I do not know of an Ellen, but the date of death and the family connection with Tuam is just a little close for comfort. She sounds very much like a sister.
This branch of the Concannon's is the senior branch, and both I and my Cousin Anthony (grandson of Austin)are the only survivors of the Derbhfinne, and, if tradition is to be followed in any meaningful way, should spend most of our time trying to poison each other for the honour of leading the family.
Happily, time has moved on and we get on very well together.
If you were in Ireland last year, you may be able to fill me in on something which I have not had the time to check. Malachy, the father of Thomas (and presumably Ellen and Mary) was born in 1852. I believe him to be the son of Edmond Concannon of Carrownacreggy, who married Kate Parsons, the daughter of the engineer who pioneered steam turbines (and by analogy, the jet engine). Edmond died in 1859 and Jane in 1854. Edmond had ten children who were initially baptised as catholics at the behest of his wife, Rachel Marshall, but were subsequently rebaptised by the new (Anglican)Vicar of Tuam. This causes some confusion which i have not yet sorted out:- Malachy remained Catholic.
In turn, this Edmond was the son of Edmund John Concannon (1792-1870) who married Jane Blake in 1815. Her Father, John Blake was an officer in the 13th Dragoons and was a member of Wellington's staff at the Battle of Waterloo in 1815. The family house in Galway was known as "Waterloo" for obvious reasons.
On his father's side, Edmond's ancestory is traceable father to son, back to the very earliest kings of Ireland, in 1600 BC (I have the details), whereas on his mother's side, the ancestory is traceable to Edward 1st of England (13th century AD).
I hope this helps and I would like to hear what you found out in Tuam last year.
In answer to your last point, yes, the Concannons do occur in other counties, but Roscommon and Galway is their home. They are of the High O'Brian sept of the Connachta, ultimately traceable to Erimon. Their seat is in the Leith Conn (i.e. the North) and were situate at Rath Croghan for the best part of two thousand years.