Kellys from Inchamore

Hi,

My great grandmother Sarah Kelly was born to Michael Kelly and Bridget Forde in Inchamore in 1885. I found the baptismal records for her and her siblings going back 1865 but I can't find the marriage record for her parents. According to the census her mother was born in 1844, but Michael was dead by then.  Michael shows up on Griffiths Valuation, along with the Cooley, Cooney, and McNamara families. I'm pretty sure the Kellys still live there judging by recent obituaries I've found online. 

However, none of these families show up in Inchamore in the Tithe Applotment Books in 1827. The Nelly, Monahan, Fahy and Lahiff families lived there but were all gone and replaced by the 1840's.

My two question are - 

1: What happened between 1827 and the 1840's? Why did all the families in Inchamore disappear and get replaced with new ones?

2: Where were the Kellys before the 1840s?  I know Galway is crawling with Kellys so it's likely I'll never know. My mother believed her ancestors were from Clare, so it's possible they lived across the border