I wanted to share this very nice (and potentially useful) map created by Kingston University, London. The Irish surnames plotted on this map have either historic or numeric importance to the counties of Ireland. Of numeric importance are the birth counts from the 1890 census. Indigenous Irish names beginning with O', Mac, Mc, De, Le, and others, indicates historic significance. The 1890 census contained over 2,500 individual surnames.
Because this map is based on a relatively late census (1890), many of the areas of historic stronghold associated with certain surnames are not reflected. A good example of this is my own surname, O'Rourke. One would expect to see this surname prominently represented in Counties Leitrim, Sligo, and Cavan. By 1890, however, the vast majority of the O'Rourkes who descended from the kings of Bréifne in that region had emigrated.
The image of the map to the left is just a thumbnail. Click on the image to see and download the full-size (50 MB) version.
I'd be interested in hearing about anything you see in relation to your own family surnames on this map. Please leave your observations in the comments section below.