In order to trace the Irish connection to an African American family; it’s first necessary to get past one major hurdle; the 1870 U.S. Census. This was the first federal census schedule to list the freed slaves by name, age, and birthplace. For this reason alone, it is among the most important genealogical resources which you can use in this type of research.
There are several factors to consider. The first is that this was only five years after the Civil War ended. The newly freed slaves were getting on their feet, and many were getting ready to move on. This means it was common for the freed slaves to be working on the very plantation they were freed from, or at least very close by. This was in a sharecropping arrangement where the freed slave would work the crops for part of the profit. Reality was usually much different. It actually differed little from slavery. Poor whites, and Tri-Racial Isolates, were also sharecroppers alongside the African Americans.
With all of its faults, abuses, and horrors, the sharecropping system at least kept families fed. It also bought families a few years of transition prior to moving far away from the old plantation. From a genealogical perspective, this means that the 1870 neighborhood where a black family was living was the old plantation itself. For our Irish Studies, this means the slave owner, who will be listed nearby in the same census can be identified. If he wasn’t the father, then you at least identified the last slave owner.
With the name of the last slave owner, this opens up surviving plantation records, and the county deeds documenting the buying and selling of slaves. Once the slave owner(s) are identified, then the way is clear to explore the Irish connection.