Its going to take me a while to go through all the posts since I've been out, but to recap on the facts as I have them
A few years ago, my aunt (Thomas's daughter) went to Ireland and tried to get his birth certificate. She was told he was not registered. She found his baptism record (no idea where but at the time I assumed it was Carrick, that being where Thomas lived his whole life and where I knew my aunt was staying). She told me then that she had discovered he was illegitimate - she was shocked, she obviously had no idea, but she did not mention the name Keegan, so I assumed he was baptised in the name McDermott, but his illegitmacy was somewhere on his baptism record.
in 1901 he is Thomas McDermott age 12 in Carrick, son of Bridget Delaney (who is step daughter to William Gallagher, husband of Margaret).
Birth details of Bridget Delaney's children give her name as Keegan.
Bridget Keegan (SPINSTER) married Patrick Delaney in 1893
Bridget Keegan gave birth to Thomas Keegan in Carrick Workhouse on 16/10/1888.
(Thomas was born in 1888 according to his family and his gravestone)
Thomas's army records give Bridget as mother, living at The Green, Boyle, and Margaret as grandmother. I remember my father mentioning Bridie, his grandmother.
Dated Jan 1908, they give Thomas's address as Kiltoghert, Carrick and his age as 19 yrs 10 mths
In 1911, Thomas is in the army, and Bridget is a widow, still on The Green, Boyle, Roscommon.
So far, everything fits perfectly.
This Thomas on census says he was born in Boyle - that is where his mother lived. He married and lived his whole life in Carrick - his obituary says he was born in Carrick.