Harry was my great great grandfather. I have been unable to find information on him before he came to America. I do know he had a sister named Cassie who also arrived in America after him. He may have had a brother named Charles and a sister Ann as well. Searching for any available information.
1855 is before the start of statutory birth registration in Ireland (1864) so you won't get a birth certificate for Henry. You might find his baptism but to do that we need his precise denomination, so as to search church records. Do you know that? Also, ideally we need his parents names from say a death or marriage certificate, to be sure of identifying the right family.