The Elusive John O. Halloran

After much research, I uncovered the naturalization certificate of my 2x GGF John O Halloran.  (Do you know how many John O Halloran combinations there are?)   In this same blog, I had posted his son’s (our GGF's) naturalization certificate of John J. Halloran.  I was able to verify from John J.’s application, the date of naturalization of John O. – and then was able to match the certificate dates in a search.  My 2x GGF John O. Halloran was a laborer and he came over from Ireland with his son, our GGF, John J in 1867.   

I did find a marriage record for John J. Halloran and Maria Haack indicating that the John J's parents were John O. Halloran and Margaret Meaney.  So who is Margaret Meaney?  Where did she come from?  What happened to John O and Margaret -- and where are they buried?