We often do not find a passenger arrival record to document our ancestor landing in North America. If the goal of my research is to find out where the family was from in Ireland, then maybe shifting the focus will help. I’ll focus on the migration pattern itself rather than a record of the migration. I know of three which I explore on a regular basis.
A group migration was common in the 1700s when families clustered in an area surrounded by like-minded people. Chances are that this group was connected in Ireland. In this migration, the group came together and stayed together. The group migration was common on the frontier where safety was an issue. So to find out where some in the community was from in Ireland is to find where your ancestor was from.
A congregational migration occurred when an entire or part of a congregation followed their minister or priest to North America. This works especially well among Scots-Irish Presbyterians. However, don’t neglect Catholics either. In these cases to find out where the minister or priest pastored in Ireland means your ancestor was geographically not far away.
A chain migration was common in the nineteenth century. In this case, your ancestor may have followed someone to the same community in North America, and in turn was followed by another. A chain migration can stretch out for decades, with everybody being from the same county or region of a county in Ireland. Communities of people from a particular county dot North America. Some urban Catholic parishes took on a strong presence from a particular Irish county as the neighborhood it served was comprised of decades of chain migrations.
Once you have identified what type of a migration pattern your ancestor was involved in; then this will open up all sorts of avenues for continued research. Often this is the only way to solve a really tough Irish research problem.