Thank you for your message.
Do you have any other information that you can share? The more information you post the more likely it is that somone will recognise the people you are researching. Also, do you know any important dates in the family? Dates such as birth/marriage/emigration dates will help establish the timeframe for your research.
You could try looking for information on Big John in church records if you know his date of birth. If you can find his birth records this will give you his parents' names also.
Most Catholic records are held locally. One website which you may find useful is the irishtimes, where they give an overview of what records are available in specific parishes. For Stradbally parish follow this link:
You could try searching for family members in the land records pertaining to Ireland in the 19th century. There are two:
The Tithe Applotment Books (1823-1838) found at http://titheapplotmentbooks.nationalarchives.ie/search/tab/home.jsp
and the later Griffith's Valuation (1848-1864) found at http://www.askaboutireland.ie/griffith-valuation/
Depending on timeframe that you are looking at, you may also be able to find some relatives in the 1901 and 1911 census records which can be found here: http://www.census.nationalarchives.ie/search/
With regards to Big John's emigration, do you know anything else about it? Do you know why he left Ireland or who he may have travelled with? Do you know where he entered the US? For information on immigration records in the US you should check the US National Archives at the following link:
It is most likely that he may have entered the US through New York, if he did you can search their passanger lists online at the following sites, and hopefully find the name of the ship he arrived on:
Ellis Island: http://www.ellisisland.org/search/passSearch.asp
For some good general information on US immigration records go to the following link:
Some other websites which you may find helpful 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
Family Search: https://familysearch.org/
Genealogy Links: http://www.genealogylinks.net/uk/ireland/laois/index.html
I hope that this is helpful. Remember to post as much information as you can with regard to the people you are researching. The more information you post, the more likely it is that one of our volunteers will be able to advise or assist you. Also include information concerning which sources you may have already used so others may further your search.