For the most part of 19th Century Parish Records in Ireland (this tradition changed in the 20th Century, when the examples above begin to apply) your starting point should always be to test the following hypothesis...
Witnesses to a marriage:
Remember that they had to be a peer and a close friend, but as much as we would like to imagine they might siblings, it turns out... 9 times out fo 10 they were first cousins. (It is also possible that one or both witnesses had a hand in introducing the couple, e.g. they were related to one party and lived near the other party, knowing this can help you lock down possible townlands of origin). Also remember, in the case of Catholic marriages, the bride had to marry in her home parish. When the groom was from another parish, the priest simply recorded the name of the parish he was from but not the name of the townland (beware, as parishes often contain a townland of the same name). There will be exceptions to this rule, but it is a helpful starting point. Knowing a possible cousin's name, allows you run a search for their own birth/baptism record. If it turns out this "cousin's" mother is a surname match, you've struck Irish genealogy gold. It's painstaking, but so worth the effort.
Sponsors to baptisms:
Keep your eye peeled for the record of 'stipend' paid to the priest for the baptism. If you see £1.10 think "wealty grazier / strong farmer". If you see 2/6, think small farmer / cottier. For these less affluent, couples (often not named on land records, yet living in a townland) followed the following Catholic godparent selection tradition to the letter. Consider every sponsor/ godparent to be a sibling or a sibling in-law of either the child's mother or father. It's that simple. The surnames that do not match the parents' surnames are in-laws and key to knocking down brick walls.
First, run searches for that unusual surname paired with the surname of the mother and then the father, to determine which side it belongs to. (familysearch.org)
Then, gather the baptismal records for that new couple, noting their godparenting choices (rootsireland.ie). Look out for a godparenting invitation being reciprocated e.g. your original father's name sponsoring one baptism and the mother another. You can then be pretty confident you have discovered another family in your tree, who may just give you the lead back to a townland or earlier generation, that you were looking for!
I have found the above traditions to certainly ring true for counties west of the River Shannon. I would be interested to hear feedback if this also applies in Co Tipp!