Hi,
Thank you for your message.
Do you have any other information on William that would help you confirm whether it is the same William in Mullingar? If you knew the names of any siblings he may have had you could cross check this with the parents names listed on the birth record. Perhaps you could try looking for his marriage record in the same parish in the hope that this was where he married?
There are a couple of places online where you could try looking for records relating to William, however again without further information it will be difficult to know whether any results are relevant:
www.familysearch.org has a huge database of genealogical records including some church records for Ireland.
www.rootsireland.ie have a large collection of Irish Church records, however you have to pay to use this site.
http://churchrecords.irishgenealogy.ie/churchrecords/ have begun a project to upload Irish church records to their site free of charge. However so far only Counties Dublin, Kerry, Carlow and parts of Cork have been covered.
Have you tried looking into his emigration? Generally more information was given at the port of arrival rather than that of departure do it may be an idea to look here. For information on immigration in the US check the NAtioanl Archives at:
http://www.archives.gov/research/immigration/
Some other websites that may be 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/westmeath/index.html
Irish Times: http://www.irishtimes.com/ancestor/
It may also be an idea to contact the Heritage Centre in Westmeath for assistance, however a fee may apply. Here is their email:
dunnasimoate@eircom.net
Kind regards,
Genealogy Support