Prior to the introduction of civil registration in the mid 19th century (1845 for non RC marriages and 1864 for RC births, marriages and deaths and for non RC births and deaths), the only place where such information would have been recorded on a countryside scale were in church parish registers.
Church parish registers are divided between RC parish registers and non RC parish registers. If your ancestors were RC, their baptism and marriage records will hopefully have been registered in the parish where the event took place. It is useful to be aware that a RC parish is different to a civil parish, and that it can have a different name and that it usually covers a more extensive area, incorporating one or more civil parishes. If you are doing your own research it is important to be aware of the difference between church and civil parishes.
However, the big problem with RC parish registers is the piecemeal nature of their survival, and even if the register that you are interested in has survived, there is no guarantee that the entry relating to your ancestor will be legible! Furthermore, standardisation of RC parish registers did not take place until the latter decades of the 19th century, or even into the early decades of the 20th century, and up to this time, details recorded in different registers varied widely. Whilst parish registers can be an extremely useful source of genealogical information, they can, for the reasons outlined above, present a frustratingly variable source varying widely from one parish to the next.
Many entries in RC parish registers are written in Latin (sometimes in English but never Irish), so a basic understanding of the most common Latin terms used in the register is useful. This is especially true where your ancestors had a surname common throughout the parish. For example, in a marriage register you might think a column headed ‘Sponsus’ refers to the ‘Sponsors’ or ‘witnesses’ to the marriage, when in fact it means ‘groom’. Further confusion can arise by the fact that in 19th century Ireland, the range of male and female forenames was limited; a significant proportion of the male population were called John/Ioannes or Joannes, while an even larger proportion of the female population were called Mary/Maria. Therefore, a bride and a sponsor, or a groom and a sponsor often shared the same forename or surname, or even both!
The date of RC parish registers differ from one parish to the next; most date at the earliest to the early/middle decades of the 19th century with a cut off date around 1900 (for online records). Although a few registers survive from the latter half of the 18th century, regrettably, few survive earlier than this date.
Notwithstanding these difficulties, RC church parish registers remain one of the most useful sources of pre 1864 genealogical information in Ireland. The RC registers remain the property of the parish church and are generally not available to the public. However, many registers are now online and are fully searchable, on payment of a small fee.
In the case of the Church of Ireland (Anglican) parish records, most of these are now held centrally in the Representative Church Body Library, in Dublin. Although many of these registers are earlier in date than RC parish registers, less of them survive as many were destroyed in the fire at the Public Record Office in 1922.