Help with a surname , please

[gaffy]

...I wonder if her name was shortened to Marg in the parish register and this was mistaken for Mary.

Pretty clearly Margaret in the parish register as well (right hand page):
https://registers.nli.ie/registers/vtls000635300#page/65/mode/1up
 

[Huckleberry3333]

Sinann that would be great but it looks like James and Mary came to the US to have their children even though I have James dying in Ireland. I am starting over so just getting my bearings..So their children in order of birth are: Maude McGrath (April 1885 Boston - no death record yet but looking), James F McGrath (21 Jan 1888 Brighton, MA but could be Woburn, MA), Eileen McGrath, my great-grandmother (23 Feb 1889 Woburn, MA - died After 1971 in Mattapan, MA), William McGrath (May 1890 Woburn, MA - 1946), and yet another Mary McGrath! (Oct 1892 Woburn, MA). For James and Mary I did have this on James (not sure it's the right james though as Mary is just listed as McGrath, not her maiden name) 
Parish Variants:   Francis St., St. Nicholas (without), Francis Street
Diocese:   Dublin

Thanks!

[Sinann]

Looking at Eileen's birth, her mother Mary Whelan was born New York so they would have married in America. Have you got the marriage?
https://www.familysearch.org/ark:/61903/3:1:S3HY-6G23-V69?i=18&cc=1536925

[Huckleberry3333]

Yes I just got it thanks!! Getting there in America. I wish I could figure out where in Ireland James F McGrath was from but that will take some time. It really could be anywhere. I'm just trying to start from scratch and only work with what I absolutely know and verify it with as many sources as I can.

[Sinann]

Did they marry 13 May 1883 New Jersey
Not allowed to see the image, have you seen it? Are both his parent's names on it? Is their an address in Ireland?

[Huckleberry3333]

Hmmmm I am not on Family Search so I have not seen that one yet. There is an image? I will log on and sign up for that. Yes, it appears they were married in New Jersey. So from what I found James immigrated over here (according to censuses of 1910, 20, 30 and 40 which I found) in either 1870 or 1881 (one census says 1870 the other three say 1881 so I think it's the latter). I think he met Mary Whelan here because I have found information leading me to believe she was not born in Ireland as I had thought but born in New York (city I think). Then they married in 1883 in New Jersey. I have yet to find anything with James' parents names on them. This is the dilemma.

[Sinann]

You have to be a member of the The Church of Jesus Christ of Latter-day Saints, or go to a FamilySearch center. Some of their records are like that.
If you're not or can't do that perhaps it would be possible to order a marriage cert.

[Huckleberry3333]

Oh! Actually there is one right near me. I'm going to try to head over tomorrow if I have time. I'll keep you guys posted! Thanks soooooooooo much for your sage advice!