Baronies were created after the Norman invasion of Ireland as divisions of counties and were used the administration of justice and the raising of revenue. While baronies continue to be officially defined units, they have been administratively obsolete since 1898. However, they continue to be used in land registration and in specification, such as in planning permissions. In many cases, a barony corresponds to an earlier Gaelic túath which had submitted to the Crown.
Corcomroe is mentioned in the Annals of Inisfallen:
907. Kl. The plundering of Lough Rí by the men of Mumu as far as Mairg Laigen and Mag Léna, as a result of which Mael Craíbe son of Cathalán, king of Cenél Fiachrach, and many others were slain. Cet, son of Flaithbertach, took the kingship of Corcu Modruad. Eight score ferryings by Cormac, king of Caisel, until they arrived in Cluain Moccu Nóis during that Christmas.
919. Kl. Death of Cet son of Flaithbertach, king of Corcu Modruad. A year of scarcity and hunger.
920. The slaying of Murchad son of Flann, king of Corcu Bascinn.
936. Repose of Aniudán son of Mael Gorm, king of Corcu Modruad.
983. A large fleet by Brian, son of Cennétig, into the territory of Connachta, and portion of his force was slain there, i.e. Mael Sechnaill, son of Coscrach, and Finn, son of Dubchrón, and Lochlainn son of Mael Sechnaill, royal heir of Corcu Modruad. His officials went by land into Uí Briúin, and great slaughter was mutually inflicted upon them and upon the Uí Brúin.
993. A naval raid by Brian, and he reached Breifne from Loch Rí by way of Áth Liac northwards. A great slaughter of the Connachta by the king of Corcu Modruad, namely, by Conchobar, son of Mael Sechnaill, and Ruaidrí son of Coscrach, king of Uí Briuin, and many others fell therein.
996. A slaughter of the Corcu Modruad in Connachta, in which Muirgius, son of Ruaidri, fell.
1003. The slaying of Conchobar son of Mael Sechnaill, king of Corcu Modruad, and of Amlaíb, son of Lochlainn, and of Aicher Ua Traigthech in the west of Connachta; and Cathal, son of Labraid, was killed by the sons of Donnchadh Finn.
1015. Death of Domnall, son of Dub dá Bairenn, in a battle against the son of Bran. Cathal, son of Conchobur, and Lochlainn his kinsman, were treacherously slain... both from their kingship. One followed the other in the kingship of Corcu Modruad. Death of Aed Ua Ruairc, king of Bréifne. The foreigners of the Isles, viz. with the complement of seven ships, raided the Islands, and they plundered Ara, Inse Mod, and Inis Aingin, and carried off one hundred and fifty as booty.
1016. The slaughter of Ára, in which Ua Lochlainn, royal heir of Corcu Modruad, was killed in Port Ciaráin in Ára. It was the Conmaicne who slew him. A great soughing wind in the autumn of the above year, and it broke down woods and houses, and people well-nigh died of terror. Death of Muiredach son of Cadla, king of Conmaicne Mara.
1017. Death of Donnchadh, son of Dub dá Bairenn. He was slain by Mael Muad.
1023. Great drought from the Epiphany until May. Ua Duib dá Bairenn was blinded. A solar eclipse this year, i.e. the spring of the black cloud.
1027. Death of Conchobar son of Mael Sechnaill, king of Corcu Modruad.
AI1094.3 The Síl Muiredaig inflicted a great slaughter on the Corcu Modruad and on the west of Connachta, and Ua Flaithbertaig, and the grandson of Conchobar, son of Mael Sechnaill, escaped therefrom.
