19-Nov-2019

We have now identified up to 9 different Costello groups with different origins and they don't appear to share any connection since the formation of the surname. Unfortunately some of our groups are quite small and the members in these groups have not tested far enough for us to identify the likely origins of their group. Below is a quick outline of each group and what we know of it.

Group 1 Southeast Ireland R1b>P312>ZZ37>ZZ38>Z30597>BY196132>BY196742>PH4705

This group has 8 members and is out biggest group so far. They come mainly from County Kilkenny in Ireland but they also spill over into surrounding counties particularly Tipperary and Waterford. We know at least two migrations of these Costellos occured to the USA, with one group leaving approximately in the 1680’s. These Costellos became the originators of the Casto surname in the USA and trace their origins to New Jersey and before that back to Kilkenny. We also know another Costello migration happened and this family became the Costley surname in the USA. It is likely there is more than one originator of the Costley surname and if you have this surname it does not guarantee that you are descended from this group but it is a possibility. Y DNA testing will confirm if your ancestors were part of this group.

Group 2 Kerry/Clare/Limerick  

R1b>unknown subclade

This Group has only 3 members and they seem to have an unusual subclade, it is also possible that their DNA is convergent as they have many hundreds of matches at the lower marker levels. The information supplied by these members indicates that this may be a group of Costellos based around the Shannon estuary as they come from Kerry, Clare and Limerick. We need other testers from these locations and also it would be great if a few of these members would do a Big Y to define their haplogroup.

Group 3 Clare/Limerick

R1b>P312>L21>DF13>ZZ10>Z253>Z2534>L226

This group only has 4 members two of whom has done a Big Y and is from the Haplogroup R-DC120 which is downstream from R-L226. The only thing we can tell at the minute is that this groups ancestors were likely to have been long in Ireland before the Norman invasion which sparked the Costello surname. The R-L21 has long been associated with Gaelic irish surnames and it is possible these Costellos adopted the name for some reason through the centuries. However until we have more testers to add to this group it will be hard to define more about it.

Group 4 possibly Ulster

R1b>P312>L21>DF13>Z39589>DF49>M222

This group again only has two members but the surname is spelt Costilow and given their DNA they are likely also a family who were in Ireland before the Norman invasion probably in the north of Ireland as the R-M222 is associated with Niall of the nine hostages and the founding of the O'Neill clan which was based in Ulster.