for reference here's a link to those births from the extracted civil collection on FamilySearch :
Buckley/McKenna-McCanna births based on the date of birth of the oldest child listed (Maria 1864), and the date of marriage you have, there would probably have been older children that could include Thomas.
To establish a more detailed location it might be an idea to start with a birth cert. e.g. the extracted record for Maria shows :
Name: Maria Buckley
Birth Date: 17 Feb 1864
Birthplace: 0214, Longford
Parents : John Buckley & Mother's Margt. Mckenna
Note - the address in these records is often a district or subdistrict, but can sometimes be the name of the county. The number in the address is the register page number, and helps locate the correct entry in the BMD Index - i.e.
Name: Maria Buckley
Registration district: Longford
Event type: Birth
Year: 1864
Volume: 3 / Page: 214
In this case Longford refers to the registration district based in the county town. You can use these details to order a research cert from the GRO, which will show some further details that should help your search back - e.g. John's occupation, and the place of residence of the family. If they lived n Longford town the address could mention a street name. If they lived in a rural part of the district it should include the name of the townland. Having a more detailed location should help establish which parish they lived in, which you need to know to search for details of older siblings and the marriage
see :
Ordering Certs from GRO Roscommon Details included on a Birth CertShane
