www.irishgenealogy.ie is a free site and the Church Tab will take you to Co. Cork church records.
The marriage of Daniel Leary and Catherine Mahony was in 1806 at Kilmurry church but no date was given just the year. One of the witnesses was a Margaret Mahony likely a sister to Catherine.
In reviewing the baptismal records, I'm wondering if there were two Daniel Leary/Catherine Mahony couples- one in Kilmurry and one in Desertserges. Kilmurry is two RC parishes north of Desertserges. I may have missed some records. My discomfort is with records in 1819/1820 and then 1824. The same couple could not have had children in two different parishes--see Jer and Julia and Patrick and Denis. The marriage record I located would apply to the Kilmurry couple. I did not find a marriage record for the parents of Jeremiah.
Let me know what questions you have.
I found the following baptismal records in Desertserges:
Ellen April 13 1818
Jer November 14 1819
Denis October 26 1824
The following records were in Kilmurry:
Mary March 7 1809
DS August 28 1814
Daniel August 28 1816
Julia February 27 1820
Patrick March 5 1824
My sense is that your family was in Desertserges based on the fact that you are in Jeremiah's line.