I may be able to provide a little supporting documentation, Bill. My gggm was Mary Gillroy. I do not have a lot of information on her, but the starting point for what I do have is the memoirs of my gggf, Simon Fitzsimmons (or Fitzsimons, or other variations.) His memoirs were dictated to his daughter shortly before he died, so there are some inconsistencies in the story. We've been able to correct some, we are still looking into others,.
My great grandfather starts the recitation that he was born in Mountpallas, in the mid-1830s. (He gave a date, we were able to confirm a slightly different date.) He goes on to say that his father was Simon Fitzsimons, his mother Mary Gillroy. (note the "ll" in the name.) Simon and Mary apparently had the following children: James born +/1830, Simon born +/- 1834, a daughter, either Mary or Bridget, or perhaps both, dob, and Partick, who "died young."
My ggf recounts living on an estate near Mountpallas, referencing a "penny a day" school across the Inny, in the shadow of Ross Castle. As a child he made a few pennies working for a farner named Rotheram. They were eventually evicted from the estate (all tenants were) when the estate went into chancery, or banruptcy. From what we can piece together, this would have been in the 1840's.
With no place else to go, the family moved in with their mother (Mary Gillory)'s brother in Thonagh (also in County Cavan, also not far from Mountpallas). I believe that Mary' Gillroy's brother's name was John, but I will try to confirm that. There does not seem to have been a lot of work there, and in about 1850 they made the decision to move to America. Simon (the younger) reports that his brother James had come to America "a couple years earlier" (1847, to Milan, Duchess County, NY) and that all of his Gillroy relatives other than the brother that they were living with, had aslo left Ireland before 1850.
Simon Fitzsimons, his wife Mary Gillroy Fitzsimons, their son "Simeon" Fitzsimons, their daughter Mary Fitzsimons and a woman I believe to be John Gillroy's daughter "Biddy Kilroy" arrived in New York in early June 1851 on the ship Jacob A Westervelt. They joined Simon and Mary's eldest son James in Duchess County, NY, at least for a while.
The two Simons (father and son) made their way west to the Chicago area by the 1870s. I had lost track of Mary Gillroy, but last year I was able to visit her grave. She is buried ion Rhinecliffe, NY, near her son James and his family. Her headstone identifies her as Mary Gillroy, wife of Simon Fitzsim(m)ons. Apparently she stayed back to help James with his young family when her husband and younger son moved west looking for work.
Subsequent sleuthing leads me to believe that Mary Gillroy was born between 1799 and 1804, based on other dates uncovered.
I'll look through the memoirs for anything else I can find relating to Mary Gillroy. I have a note that her father's name might have been John, but I'd want to verify that source before you dive too far in to that. Note also that the records I have reviewed have spelled the name Gillroy, Gilroy, Kilroy and Gibney. Three of those are phonetic spellings, the last a transcription error, I suspect.