Originally, it was Ó hEachighearna, meaning lord of the house. It became O Hagerin in English, which in time changed to Ahern or Hearne. The name is originally Dalcassian, from a sept which migrated from east Clare to Co Cork. In the 10th century this was an important sept, whose chieftain was Mathghamhain, King of Thomond; an elder brother of the Irish High King, Brian Boru. The territory of the King of Thomond at that time covered Co Clare and parts of Co Limerick. Today, there is no clan chief and no family seat. However one place that has the name and has many historical resonances is Hearn's Hotel in Clonmel, Co Tipperary. Ireland's first ever public transport system, started here in 1815, the Bianconi mail coach service.

Among well-known holders of the name was Patricio Lafacadio Hearn (1850-1904), a journalist who emigrated to Japan in 1890 and spent the rest of his life there. He explained Japan to the western world, the first person to do so and accordingly, is greatly honoured in Japan today.