siblings of Mary (Blanchfield) O'Neil in the Northhampton area:
Ellen Blanchfield Crotty, death, 1897
https://www.familysearch.org/ark:/61903/1:1:NWWY-868Michael Blanchfield death, 1904
https://www.familysearch.org/ark:/61903/1:1:NWLK-4BTMargaret Blanchfield marriage, 1866 Northhampton
https://www.familysearch.org/ark:/61903/1:1:N4QD-JCK-------
ancestry suggests the marriage of Timothy Blanchfield and Mary Walsh, 26 July 1818 in Drangan, Tipperary. the image and transcription give their townlands.
https://search.ancestry.com/cgi-bin/sse.dll?dbid=61039&h=8749911&indiv=try&o_vc=Record:OtherRecord&rhSource=2101ancestry suggests the death of Timothy Blanchfield, age 80, in Carrick-On-Suir, Tipperary, in 1866.
https://search.ancestry.com/cgi-bin/sse.dll?dbid=2534&h=680819&indiv=try&o_vc=Record:OtherRecord&rhSource=2101https://civilrecords.irishgenealogy.ie/ says it was the 1st quarter of that year and gives the information for ordering a copy.
Don't jump to conclusions that this is the right couple and death. There might have been more than one couple with those names in Ireland in that timeframe, and not all the parish registers are online. But if you can find a few of the baptisms for Timothy and Mary's children that match the people in Northhampton, then you can be pretty sure.
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probably all your family:
1885 Northhampton City Directory
Blanchfield
Alice, widow of Edmond home on State
Edward, laborer, home on State, north of Park
James, removed [moved] to New York
Mary, widow of Timothy, boards at the Cook House, Main, Leeds
Michael, watchman, home on King
Michael W, clerk, home at 18 Cherry
Thomas M, removed to Easthampton
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Michael W Blanchfield, d 8 October 1903, age 50, Northhampton, son of Edward Blanchfield and Alice Nugent
https://www.findagrave.com/memorial/113662427/michael-w-blanchfieldEdited. Correction:
There is no double "h" in the middle of Northampton, Mass. It will affect your searches, at least at ancestry.