I'm more specialised in EM Scotland but there is some overlap with EM Ireland and I have studied EM north-west Europe more broadly so I feel qualified to give you some kind of answer.

It is my understanding that there were no cities in EM Ireland. Social organisation was overwhelmingly rural and decentralised, with communities loosely clustered around power centres, some of which would later become towns and cities. Dublin is the exception- it grew quite rapidly into a proto-urban centre comparable to contemporary settlements in Scandinavia such as Birka, and was an integral part of the Scandinavian maritime trade routes. Urbanisation didn't take off in north-west Europe until the Mediaeval proper. Beginning in the Late Iron Age and really kicking off in the EM was a centuries-long, gradual process of increasing political and economic centralisation towards trading, secular and ecclesiastical power centres, which in turn led to a greater concentration of wealth and resources around these centres, many of which would later become cities. This went hand-in-hand with the consolidation of territory, the growth of kingdoms and the increasingly far-reaching influence of the church, which eventually led to fully-fledged states. Further, advancements in agricultural and maritime technologies meant that larger and more reliable sources of food became available, leading to a population boom that grew the new cities.

It's worth noting that the population of this region really stayed predominantly rural and agricultural until the Industrial Revolution, though denser populations (and often more prestigious power centres) could be found in more fertile areas or those particularly well-suited to serving maritime trade routes.

Since u/kirstybaba has already answered your question, I will just say that if you want to learn more about the social structure and economy of medieval Ireland, the Dublin Institute for Advanced Studies has a series of books called the Early Irish Law Series that is very interesting. Early Irish Farming is a great starting point and touches on a lot more than the title might suggest.