Hello Ron,
I went to www.rootsireland.ie and found the marriage record for Denis Corkery in the parish that you named. I tried to locate his baptismal record but I could only find two records for a Denis Corkery in Co. Cork 1815 and 1816.
I am wondering where you found a record for an 1811 birth? If it comes from a tombstone or census record then I would advise a little caution regarding the dates.
Most people who emigrated were illiterate and undocumented. They didn't know how to spell their names and hadn't a clue as to what age they were. At the port of arrival their names were recorded phonetically, their ages were only guessed, and this is the information that followed them for the rest of their lives.
The proof of this occured in 1909 when the old age pension was introduced into ireland. People had to prove their ages and were forced to go through baptismal records to establish when they were born. That is why there is such HUGE discrepancies between ages in the 1901 census and the 1911 census of Ireland. Dates were found to be out by many many years in some cases.
We tend to forget that people back then had no social security numbers, and were not tracked from the cradle to the grave as we are today. They didn't celebrate birthdays, as it was all they could do to clothe and feed themselves. So I would advise that people bear this in mind when researching.
If you have (or are going to purchase) the marriage record, is there a parent's name on it?. In many cases you will find a father's name. Once you have a father's name it will go a long way in determining which of these two records is the baptismal record for Denis.
When you get the baptismal record, it will contain both parents' names. You will then be able to search the baptismal files ( leave the first name blank on the search bar, but fill out the parents names) and you will know what siblings if any that Denis had. At least then you will know for sure if he had brothers or sisters that may have had families of their own. This search can only be done on the main menu page not the county genealogy pages.
If I can help in any way, or if I haven't explained correctly, please let me know and I will try to help.
The place to start is the marriage record to see if there is a fathers name.
Anne Dennehy