Laurence or Lawrence Keenan

I am looking for which parish/ village/ town that Laurence Keenan may have come from.  We are planning a trip to Ireland around Sept 2015 and would like to do some further research.  Much of the info I have is from a document called the Catholic History of Indiana.   The relevant parts are below:

JAMES H. KEEN AN ( my great grandfather) is a member of St. Anthony's parish and 
a representative Catholic citizen of Indianapolis. His father, 
Thomas Keenan, was born in Monaghan county, Ireland, in the 
year 1815, and there grew to manhood, learning the trade of stone- 
mason. In 1850 Thomas Keenan married Miss Ann Hanlon, a 
native of the same county. 

Lawrence Keenan, the father of Thomas, and John Hanlon, 
the father of Ann, were prominent, well-to-do and highly respected 
farmers, possessing more of this world's goods than fell to the lot 
of the majority of their countrymen of those days. Mr. Hanlon, 
particularly, was a man of much ability and energy, and was very 
prosperous. Both were devout Catholics, leading lives of excep- 
tional purity and uprightness, and were earnest workers in the 
cause of religion in their respective parishes. They reared and 
educated their children with extreme care, and had the satisfaction 
of seeing them develop into good men and women and practical 
Catholics. Ann was the oldest child of John Hanlon, and inher- 
ited in a marked degree her father's natural ability, force of char- 
acter and high sense of honor, as well as fine personal appearance. 
Soon after their marriage Thomas Keenan and his young wife came 
to the United States, locating in Providence, R. I., where he 
engaged in contracting for stone work. 

Note that Thomas's birth date in various US documents varies from 1815 to 1825.  It is also clear that he came to the US with or after his brother, James, also from County Monaghan. His birthdate is listed as Oct 1822.

In Thomas's death certificate lists Jane as his mother.

So in summary Laurence or Lawrence and Jane Keenan lived and probably died somewhere in County Monaghan.  They had at least two sons, Thomas born between 1815 and 1825. More Probably 1825. The other son was James born 1822.  All born in Monaghan.  Thomas met and married a woman from Monaghan Ann Hanlon whose father was John Hanlon around 1850.  All from the same county.  And then Thomas and Ann, separately or together sailed to the US between 1850 and 1852 as they had their first child in the US in 1852.

You would think that would be a lot of information but I have been stumped for years on the next step of where did Laurence or Lawrence and Jane Keenan, and Thomas and James Keenan, and Ann and John Hanlon come from in County Monaghan.

All hints and help are welcome.

Thanks.