Hi,
Thank you for your message.
Have you ever tried looking the family up on Family Search? This is a huge database of genealogical records. I did a search for a John Duffield with Margaret McGaw and found their marriage record. I also found a birth record for a Mary Ellen Duffield born 1864 to John Duffield and Margaret McGaw Duffield. Do you think this could be a sibling of John Henry? If you would like to see the results of the search follow this link:
https://familysearch.org/search/record/results#count=20&query=%2Bgivenname%3Ajohn~%20%2Bsurname%3ADuffield~%20%2Brecord_country%3AIreland%20%2Bspouse_givenname%3Amargaret~
It may be an idea to look into Church records yourself to see if you can find any more information. Most Catholic records are held locally. One website which you may find helpful is the Irish Times where they give an overview of what records are available in specific parishes. For parishes in Antrim follow this link:
http://www.irishtimes.com/ancestor/browse/counties/rcmaps/antrimrc.htm
For Church of Ireland records check http://ireland.anglican.org/about/42 and http://www.nationalarchives.ie/
As Civil registration records began in 1864 you may also be able to find any records pertaining to the family after this date. these records are available from the General Registers Office in Dublin (http://www.groireland.ie/research.htm )
You can search the indexes to these registers online however, here: https://familysearch.org/search/collection/1408347
If you would like to see if there were any family still in the area at the turn of the century you could check the 1901/1911 census records here:
http://www.census.nationalarchives.ie/search/
Some other websites that you may find useful are:
The National Archives of Ireland http://www.nationalarchives.ie/genealogy1/genealogy-records/introduction/
The National Library of Ireland http://www.nli.ie/en/family-history-introduction.aspx
The National Archives UK ? genealogy search: http://www.nationalarchives.gov.uk/records/looking-for-person/
The Public Records Office of Northern Ireland http://www.proni.gov.uk/index/family_history.htm
Genealogy links: http://www.genealogylinks.net/uk/ireland/antrim/index.html
I hope some of these links are helpful to your research.
Please be patient - as our programme has only begun to rollout across the island of Ireland and volunteers in some areas may not yet be organized.
Kind regards,
Genealogy Support