Hello Kathleen, I can find no birth in Ireland to a Corbett / Holmes from 1790 to 1810, there are 13 baptisms with a father Thomas but no Cornelius, where did you get this information as Roots Ireland do not have it and it is unusual to get records back into the 1770s.
I found the marriage you mention in 1841 in Ballyhea, this would make him 38 getting married, also found the 3 children, all from Roots Ireland a subscription site. Ballyhea is a good distance from Cobh so why do you think they moved, no trains etc then, unless he moved to another part of the landlords farm etc (they owned huge amounts of land by current standard
There are also two children born in the period checked to a Cornelios Corbett and a Catherine Duane; could not locate this marriage but found a marriage again in Cork of a Cornelius Corbett and a Grady lady in 1835, assume you are identifying him from the children and his death records, but it is tricky standing up Irish records for this period.
I attach the records found for the family you mention, searched from 1841 to 1853 as assume they left then. There is a Cornelius Corbett in Griffths Valuation in 1851 in Ballyhay, townland Pruntus, assume this is your land and this site you can plot exact plot he lived on but a bit tricky on the maps, he rented the land, see http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearch
You can use this site to find places and see the distances here https://www.townlands.ie/cork/ Assume. it is Prohus on this site, think there are two of that name so use the map to see which is in Ballyhea, think it is this one https://www.townlands.ie/cork/ballyhay/ardskeagh/pruntus/
You will probably require a car to visit here, but other places as I said are reachable by train.
Regards
Pat
