I am one of the FTDNA admins for the R-L226 haplogroup project which is one of three known Irish only haplogroups. L226 is Dal gCais in origin and Sir Conor O'Brien, a direct male descendant of King Brian Boru belongs to L226. There are eleven McGrath testers to at 67 markers. One branch (DC201) is genealogical in nature since 17 of 19 testers are either McCraw, McGraw or McGrath. Other branches including McGrath include: DC63, DC106, DC205, FGC12296 and FGC12290. We now have 46 branches under L226. Of the 522 testers, 80 % of testers with any ties to Europe are found in five Irish counties: Clare, Tipperrary, Limerick, Kerry and Cork. Another 10 % are in the rest of Ireland (probably recent movement within Ireland). The remainder are primarily in England with a few in other countries.
L226 is one of the most researched haplogroups in the world with 522 testers at 67 markers and around 25 % have tested around 40 to 45 known branches. This allows us to now chart the connections between 80 % of the testers:
http://www.rcasey.net/DNA/R_L226/Haplotrees/L226_Home.pdf#Page=22You might want to consider testing 67 YSTR markers at FTDNA to see if you match these McGrath or McGrath variant surnames. If you do match, you can contact your matches via email to exchange traditional genealogical sources:
https://www.familytreedna.com/products/y-dna
