I searched the subscription site Roots Ireland and located the marriage record for William Fenton and Ellen Neligan in the Doneraile RC parish which is the parish north of Killavullen (Annakissy) which was the parish where Henry was baptized on July 23 1844. There were no baptismal records for siblings to henry so maybe they left Ireland soon after he was born.
Have you taken a DNA test? If not, I would consider a test. You may have matches with others with Fenton connections.