The Offaly family take their name from Conchobhar (d.979), who claimed descent from Cathaoir Mor, a second-century king of Ireland. They remained powerful in their original homeland until the sixteenth century, when they were dispossessed of their lands.
The O'Connor Kerry were chiefs of a large territory in north Kerry, displaced further northwards by the Norman invasion to the Limerick borders, where they retained much of their power down to the seventeenth century. Today, the descendants of these O'Connors are far and away the most numerous, with the majority of all the many O'Connors in Ireland concentrated in the Kerry/Limerick/Cork area.
However, the most famous of all the O'Connor families is that which arose in Connacht. The ancestor from whom they take their surname was Conchobhar, King of Connacht (d.971), and direct ancestor of the last two High Kings of Ireland, Turlough O'Connor and Roderick O'Connor, who ruled through the twelfth century. Unlike the vast majority of the rest of the old Gaelic aristocracy, the O'Conors of Connacht managed to retain a large measure of their property and influence through all the calamities from the seventeenth century on. The line of descent from the last Chief of the Name is also intact; the current "O Conor Don", recognised as such by the Chief Herald of Ireland, is Denis O Conor, Jesuit priest. The family seat remains in the ancestral homeland, in Castlerea, Co. Roscommon.
The arms of the family reflect the large role which pre-Christian traditions play in the arms of Irish families; trees, in particular the oak, the yew and the ash, possessed mystical significance in Celtic religion, with the oak in particular strongly associated with the power to rule - the ring-fort homes of the ruling families of Ireland up to the early middle ages are almost invariably described as having a sacred tree outside the wall of the rath. As a symbol of kingship, then, the oak-tree of the O'Conors is peculiarly appropriate. It is also significant that many of the other Connacht families connected by descent or association with the O'Conors display the oak tree in their arms, though generally in a modified form.
Charles O'Conor of Belanagare (1710-1791), of the Roscommon family, was one of the most famous antiquarians of the eighteenth century. Roderic O'Connor (1860-1940), also originally from Roscommon, was a painter who exhibited with Van Gogh, Toulouse-Lautrec and Seurat in Paris in the 1880s, and became a close friend of Gauguin. He followed his own path, belonging to no school, and since his death his reputation has continued to grow.
James Charles O?Connor (1853-1928) came originally from Cork, but settled in Germany where he became prominent in the promotion of Esperanto . Among the many works he published was a translation into Esperanto of the Gospel of St. John.