24/09/2026
Before the counties were drawn there was a kingdom called Breifne, and it covered what is now Cavan and Leitrim along with pieces of the ground around them.
It was ruled first by the O'Rourkes and then split, with the O'Reillys taking the eastern half, which is roughly modern Cavan, and the O'Rourkes holding the west, which is roughly Leitrim. The two families spent several hundred years in a rivalry that shaped every other family in the territory, because smaller lineages had to attach themselves to one side or the other, and the gallowglass MacCabes were brought in to serve both.
It is drumlin country, a landscape of small round hills, small lakes and bad roads, and it was never rich. What it produced instead was an unusually distinct set of surnames, names that barely appear anywhere else in Ireland and that place a family almost exactly when you find one.