I searched the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800.
Note 1 - Without a KNOWN parish, the chance of an ancestor's rcds NOT being in this database is AT LEAST 35%.
Note 2 - Only 1/2 of Co. Cork's rcds are in this database.
Note 3 - The RC church kept control over most parish rcds from Tipperary (north). These are ONLY available thru the Tipperary Family History Research center at a substantial fee (regardless of outcome).
For Bridget Tallon B 1820 in Co. Meath with a father named James, I found 1 B rcd.
For James Tallon B 1817 ditto, I found 1 B rcd.
For John Tallon B 1812 ditto, I found 1 B rcd.
For George Tallon B 1807 ditto, I found 1 B rcd.
For James Tallon M 1803 +/- 1 yr in Co. Meath, I found couldn't find earlier M rcds.
Google the Foundation's name to lead you to this database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.