Mulvihill family

My great great uncle Dennis Mulvihill was baptised in the Carrigeen townland, civil parish of Shankill, RC parish of Elphin, Co. of Roscommon, in 1839. I am looking for information about the townland in 1839 and why they may have been there. I have checked Griffith which is a few years latter, and the records show only 4 families in the area, and no Mulvihill's. It looks like the area was a farming area.

Dennis's brother Thomas was baptised in 1844 and the family then lived in Mantua , Brackloon townland Civil parish of Shankill, RC parish of Elphin, Co. Roscommon.

Their Parents were:

Thomas Mulvihill born 1813,

Mary Freeman born 1813. No record of their marrige has been located.

I know the family move the Essex County, New Jersey sometime in 1847 where they had two daughters Ellen and Mary.