This is what the South Mayo Family Research Centre came up with.
They reckoned the RC parish was Crossboyne and Tagheen. They found a Patrick McDonagh married Ellen Walsh on 5th March 1843. Patrick's date of birth can be estimated by his age shown as 48 on the 1871 census in Liverpool, so they conclude he was born around 1823.
There were 3 sons. First John, baptised 25th July 1852 in the same parish. Godparents Pat Walsh and Mary Caw.
Second Patrick, baptised 4th March 1855, godparents James McArdle and Catherine Cunnane also in the same parish. Third son, Michael McDonagh baptised 1st June 1860, godparents Patrick Walsh and Judy Duignan. This third child was baptised in Kilcommon RC parish.
The townlands in this area they think most likely are Derryfada Lower and Derryfada Upper, within the parish of Tagheen on Griffith's Valuation.
The family first show up in Liverpool on the 1871 census. Ellen Walsh has died by then, so Patrick, the father of the family who was born around 1823, has already remarried in Liverpool on 23rd September 1868. The new wife is Mary Joyce .This second marriage certificate shows Patrick's father as John McDonagh.
I think it was the South Mayo people who came up with the name 'Derryfad', rather than it being a family tradition that they were from that particular place.
