Crehan in Limerick

Hello,

My 2nd Great Grandmother was Mary Ann Crehan from Limerick.  Unfortunately, I don't have any paper trail proving this, just what was told to me by my father who spent many years on our family genealogy.  Mary Ann was born in 1849 "in a town near Shannon Airport per my father's notes" and emigrated to Pottsville, Pennsylvania in 1863 and I don't know if she came alone or with family. Per the Grenham site there were 9 families scattered about Limerick with three spelling variations: Crehan in Bruff, Emlygrennen, Killeenagarriff; Creahan in Caheravally, Caherelly, Kilfrush; Crean in Hospital, Killeenagarriff.  A Pennsylvania census and death certificate imply there might also be a family connection to Limerick Hazletons - three families are found in St Michael, St Nicholas and Donaghmore per Grenham site.  

What can you tell me about the Crehan and Hazleton families in Limerick?  Are there families still associated today with the parishes mentioned above or elsewhere in Limerick?  And are there parish records available for the time period and are they available online?  

Thank you in advance for your help.

Monica Hobbs