John Henry - Pollomalady Lurgan

Hello!

I am new here and looking for any information/guidance on researching my ancestors. 

My great-great-great-grandfather's name was Ralph Henry, he was born in 1833 in Ballyjamesduff in Cavan and was Presbyterian. His birth record shows John Henry and Frances Clemenger as his parents. I found that John and Frances were married in 1816 in Kilmore, Cavan (with Church of Ireland listed, not presbyterian). In the 1821 Census I found John and Frances Henry living in Pallomalady, Lurgan, Cavan. Based on the info on the census, John's birth year would be 1793 and Frances' would be 1798. I also find them in the 1825 Tithe Appointment Books in Lurgan. They eventually moved to the US in 1848 and I see them on the census there with Ralph, my great great great grandfather. I am able to find Frances' birth record and family in Cavan, but I am having no luck with John. I have been using the rootsireland website, ancestry, and myheritage with no luck! I can find birth records for a John Henry around his birth year but none are in Cavan and most of them are Roman Catholic which wouldn't add up. I have a lot of Scottish in my DNA and I'm wondering if he could have moved from Scotland to Ireland and that's why I can't find his birth records in Ireland? I don't know how to even start searching for him in Scotland with no information about his family (siblings, parents, etc), knowing only his birth year and name - and Henry is a very common name!

Do you have any suggestions on where to go from here? 

Thank you so much!