R1b-L21 Y-snp frequency by province

As most of you should probably know, the vast majority of Irish men (nearly all of them in some counties particularly in Connaught) will be downstream somewhere of R1b-M269, most likely belonging to the L21/M529 subclade. Once upon a time during the dark ages of population genomics it was believed that this particular haplogroup spread with post LGM hunter gatherers who migrated from the Franco-Cantabrian refuge during the pleistocine/holocene transition, known as the Bolling-Allerod warm period, which saw temperatures soaring before they plummeted again to LGM levels during a period known as the younger dryas. This theory was popularised for a few years by geneticists such as Stephen Oppenheimer and Brian Sykes whom came to the conclusion that the inhabitants of Britain and Ireland where predominantly the descendants of these people, an assertion now proven false.
It appears now thanks to improvements in technology within the field, that the source of R1b-L21 derived haplotypes and autosomal dna in Ireland can be attributed to the beaker people that arrived 4500ybp.

The subsequent founder effect resulted in the replacement of nearly all previous neolithic paternal lineages on the island (predominantly I2a2a1 see here) with the phylogenetic landscape remaining relatively unchanged over the next four millenia, no thanks to the clan system which ensured the dominance of this Indo-European line. Only the Basque have a higher proportion of haplogroup R1b.

As you can see later migrations of vikings,normans,gallowglasses etc left their mark, but these groups integrated relatively quickly and even amongst modern surnames with norman and viking origins R1b is still interestingly quite prevalent. 

During the Bronze age it seems that the most common terminal snp was probably R1b-DF21 found in Rathlin 1 (tall blonde fella they found round the back of a pub) which is most commonly found in men with surnames such as O'Carroll, Dooley, Bowes and Flanagan to name a few. Overtime this lineage was overtaken by later founder effects during the Iron age (most famously R1b-M222 associated with the O'Neill clan and found in over a million Irish men) due to various bottlenecks which saw the population shrink probably due to a cold spell at the time.

In no particular order, L21/M529 peaks in both Connaught and Munster at around 73% each, followed by 70% of men in Leinster and about 61% of men in Ulster.

So it seems like men in those two provinces were cucked harder over the years, for obvious reasons.

These numbers are based off of Family Tree DNA databases and the 2011 Busby et al study, which might be somewhat dated, however I believe these numbers to be fairly accurate.

More or less.