There exist a few potential O'Reillys; we know of chieftains there, but not who exactly was the one in charge with any clarity until the early 1100s (which doesn't mean much, since, while we know who his dad was, the way Irish inheritance works, he could've as easily become king of the area from inheriting from an uncle, a cousin, a brother, a grandfather...).
Terrain, Corcaigh should be a marsh (the area around the city was a marshland, 'Corcach', whence came the name of the city). Brega should be a plain, An Cabhan could be hills, marsh, or plains (the area covered varied quite heavily between the three at the time, though over time many of the swamps were drained).
Corcaigh itself could probably do with its own ruler, a member of the Ui Caim, Ui Donnchada, Ui Murchertaig, Ui Suilleban, or Mac Cartaig probably, with claims on Desmumu and the duchy of Munster (they were all Eoganacht clans, who had been deposed of rule of Munster by Brian Boru and his family, and were centered with some other tribes in the south, until they later regained rule of the territory, united under the MacCarthy Mor). They were semi-independent and were the majority of the controlling merchant families in Cork at the time as well, along with MacLochlainns and a few other Norse-origin families. Though, it may be fruitless given how many kids Toirdelbach has, and how the AI works (instantly snatching up areas from vassals to replace them with their adult sons). Though, if we talk big map again sometime soon, we could come back to that concept, since there's a lot of territories and tribes in the south in what is mostly Desmumu right now that'd be pretty cool to have a second look at, on a smaller scale map.
