County Dublin (Baile Átha Cliath, "the town of the ford of the hurdles")
Dublin has long been a place apart from the rest of Ireland. It was founded in the eighth century by the Vikings and remained a base for their commerce and raiding until the decisive defeat of the battle of Clontarf in 1014. Although their military and political power waned, Dublin remained an essentially Viking city for a further two centuries. It was only when the invading Normans made the city the administrative centre for their activities in Ireland at the end of the twelfth century that its importance began to grow. For the following six hundred years Dublin remained the focus of Norman and English power in Ireland, and essentially foreign to the vast majority of the native Irish. In the nineteenth century, the population grew and changed rapidly as poverty, disease and overpopulation drove small tenants and landless labourers into the city in search of employment. By the early years of the twentieth century, the city had trebled in size and had some of the worst slums in Europe. Since independence, the city has continued to grow in both size and diversity and the majority of its inhabitants are now either migrants from elsewhere in the country, or the children of such migrants.
When researching ancestors from Dublin, it is important to keep in mind that the city as it is now is relatively recent; until the middle of this century there was a large rural population in the countryside surrounding the metropolis, and the records relevant to researching that population are essentially the same as those for any other part of the countryside, even though the places where they lived may now be fully a part of the city.
Given its social history, there are a very large number of surnames common in Dublin, though few which originate there. The most common are those which come from the areas immediately adjoining the county - Byrne and O'Toole from Wicklow, Dunne, Behan and Moore from Kildare, Reilly, Lynch and Brady from Meath.