William John McNeilly was born 1838 and died 1905 in the Ballymena area, N Ireland. He had a son David who was born about 1886 so it is not likely to be yours.
There are a lot of McNeilly families in this area and some of them went to Americia. I was always told that 3 brothers of my Great Grandfather went to the USA and I have a letter from a Great Uncle Robert McNeilly who in 1864 was staying with an Aunt & Uncle in the Glendive, Montana area but I do not know whether they McNeillys or Gillespies which was my Great Grandmothers name. There was also a son James and a daughter Hannah in this family.
Sorry I can't be of more help