Hi, Stephen. I can add some more info to what Roger and Shane found. Using the birth record which he found, I located the baptismal record for John McDonagh (August 14, 1870), and am attaching a copy here (he was baptized at the church in Kiltimagh – the main parish town).
Note that the birth record is from the Swineford registration district, but that does not mean that the family lived in Swineford/Kilconduff parish. Civil records of births started in 1864 (for Catholics), and the civil registration districts were large areas covering several parishes, and simply took their names from a major local town. The record which Roger located clearly shows the family’s home townland as Killedan (which bears the same name as the parish of Killedan). I can tell that, because the Honora Gallagher whose birth is listed further down on the page is a distant cousin of mine, and is correctly shown as being from the townland of Comdera (Comderry), also in Killedan parish.
My (Gallagher) grandfather grew up in Killedan parish, in a townland called Carrownteeaun (Carrantiane), which is actually separated from the townland of Killedan by just one other townland, Rathslevin, and there were also McDonagh’s living in Carrownteeaun, as well as in the nearby townland of Treenageleragh. There were several Gallagher-McDonagh marriages there in the 1800’s, so we might even be related (have you done DNA testing?). You can see more info about Killedan township at this link:
https://www.townlands.ie/mayo/gallen/killedan/killedan/killedan/
To add to the census info which Roger sent you, here is a link to a similar 1901 record which shows, in addition to Bridget and her family (presumably some of her adult children), another McDonagh family living there at the same time, headed by a Pat McDonagh, with his wife and infant son. Pat was very likely another of Bridget’s children (likely the same older brother Pat whom Roger found):
http://www.census.nationalarchives.ie/search/results.jsp?census_year=19…
Since Roger found a death record for Bridget’s husband, Nicholas, in 1900, that explains why he is not shown with the family in the 1901 census.
I’ve also located another potentially related record. In Griffith’s Valuation (mid-1800’s), there is just one McDonagh listed in Killedan township, a Michael McDonagh:
https://www.askaboutireland.ie/griffith-valuation/index.xml?action=doNa…
That Michael is very likely the father of Nicholas McDonagh, who would himself have probably been too young at the time to hold a tenancy, but probably inherited it when his father died. So, that may take you back another generation. There were earlier censuses in the 1800’s, but most of the records were destroyed in 1922, during the Irish Civil War. They can sometimes be found in 20th century old-age pension records (which were not destroyed), since people often used copies of the old census records to prove their ages, but unfortunately the pensions started in 1909, and Roger has found a death record for Bridget in 1907.