It depends on their religion. If they were Catholic, then the Catholic church records are available at Ancestry, FindMyPast and the National Library of Ireland. Many only go back to 1820 or so.
If they were Protestant things are not simple. Many Anglican/Church of Ireland were destroyed in 1922. There is no one site for these records. Here I recommend John Grenham's site
https://www.johngrenham.com/places/ which lists the available records for each town and religion.
Protestant marriages were recorded by the state starting 1845, some of these are on FamilySearch.