There were no Jacobs in Lullymore in 1901 and 1911 Irish census, these censuses are now on line, just google Irish census on line. You can actually view and print the original hand written census form completed by the family.
There were Jacobs in 1901 and 1911 in Lullybeg, they were neighbors of my great grandfather Peter Fitzpatrick. My Grand Mother and my Mother often mentioned them. I feel sure they are most likely your Ancestors.
Incidentally Lullybeg is close to Lullymore. It was a bog island containing a number of small farms, Bord Na Mona purchased all these farms (complete bog island) about 50+ years ago and the road into it is now gated and overgrown.
copy of online census attached.**
Best of luck with your search.
Terry.
** Moderator's Note- census page removed- please see
here