I search the IFHF's online database at ROOTSIRELAND.IE. It has abt 19 million B/M/D and other records for MOST Irish counties. Records before 1863 are increasingly sparse. By 1800, they are almost non-existant. Many B/M/D events either weren't recorded, or haven't survived.
For a John Denning B 1830 +/- 5 yrs, Co. Cavan, with the parents' names unknown, I found 1 record: 1835.
For a Mary McGillick B ditto, I found 10 records: 1-1830, 2-1832, 2-1834, 2-1835, 2-1836, and 1-1838.
For John McDonnell B ditto, I found 4 records.
For Bri(dget) McDonnell B ditto, I found 2 records.
Obviously there are many false positives. Suggest you find better estimated DOB, placenames, and/or parents' names to determine which, if any, of the above are for your ancestors.