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Bapitsmla records for Ardrahan RC parish start on May 30, 1839 so if Mary Anne was born on February 2, 1839 a baptismal record would not exist unless she was baptized in another parish. I searched in the Galway West records on Roots Ireland and although there were many Mary Brennan records, the 1842 transcription below was the only one in Ardrahan. You will need some info from American records to determine if this is your ancestor or another Mary Brennan. Here is a link to the parish register. http://registers.nli.ie/parishes/0611
Name:Mary BrennanDate of Birth:
Date of Baptism:18-Jul-1842Address:
Father:Martin BrennanMother:Anne DonohueOccupation:
Sponsor 1 /
Informant 1:Patrick CoenSponsor 2 /
Informant 2:Mary Coen