Couple of things Micki:
First the obituary of Captain William H Griffin (son in law of Margaret Shanahan) through her daughter Johanna. The Captain died at his home at 78 West Mohwak St., Oswego, NY in 1913 and is buried like his mother in law Margaret Shanahan in St. Paul's RC Cemetery in Oswego, NY.
I then found a biography of the Captain and it has some very interesting information regarding his wife and her parents including giving Margaret's maiden name - QUINN. This page states the following:
"On December 10, 1868, Capt. William H. Griffin was wedded to Miss Julia, daughter of Michael and Margaret (Quinn) Shannon, of Oswego. The children born to this union were: Andrew J., an engineer, who met an accidental death on the Rome, Watertown & Oswego railroad, April 18, 1896; Michael J., second mate of the steamer Monteagle in 1897; Frank H., now wheelsman of the Monteagle; John, second mate of the same steamer; George, who died young; Etta Mary, now the wife of Thomas W. Whellahan, and Robert. There is also a granddaughter, Lilly. The family homestead is pleasantly situated at No. 78 West Mohawk street, Oswego, New York."
Now, several things are wrong with this of course, we know Captain William's wife's name is Johanna not Julia (it's given that way through ALL their census records) and we also know that her maiden name is Shanahan not Shannon (it's that way on all their census records too EXCEPT for the New York, State Census of 1875 where Margaret and her son Dennis are listed as SHANNON. But the clincher is of course that address and all the children's names being correct, etc.
Armed with that maiden name of QUINN for Margaret, I took a look at my Shanahan marriage records extracted from http://www.rootsireland.ie and found a marriage that took place in 1841 between Michael Shanahan and Margaret Quinn in the Roman Catholic Parish of Templemore. I'm not sure what all the townlands that lie in that RC parish are, but I'm sure you can find out or someone here on this board can assist you in determining the townland names.
Meanwhile here are some other records you will want to check out:
Obituary of Edward Joseph O'Brien Violet Cecelia Daly's husband (they had offspring so you must have O'Brien cousins out there somewhere!)
Obituary of Dennis Shanahan of Ashtabula Dennis apparently served during the civil war as an Engineer in a New York Regiment as there is a Mention of Civil War Pension that he filed for in Ohio since that is where he was living at the time. This pension is confirmed at https://familysearch.org/pal:/MM9.1.1/QJDP-4GZR although I've yet to find him in the Civil War Soldiers and Sailors database.
1850 Federal Census for Michael and Margaret Shanahan (It's got Margaret missindexed as Maryanne, but it's as plain as the nose on your face when you view the original that it says MARGARET)
Charles H Daly 1883-1931 burial location (child of Mary Shanahan and Patrick J Daly)
Mary Shanahan and hubby Patrick J Daly in 1915 NY State Census Patrick J Daly is widowed by 1920, so Mary died between 1915-1920 but I've yet to find her death record.
Have lot's more links on census records and stuff, but I imagine that you've already got those things; if not just give a holler. And let me know how you progress and if you can confirm the QUINN maiden name of Margaret.
Kathy
GGgranddaughter of Michael Shanahan (of Co Tipperary and Co Limerick and Mississippi USA)