• 14 members

About us

Historians state that McOsker – MacCusker – MacCosker are principally a branch of the MacGuires in County Fermanagh, in Northern Ireland.

We believe that we are descended from Oscar Mag Uidhir, (pronounced mag uwarr) the great-grandson of Donn Carragh Mag Uidhir, the 1st Prince of Fermanagh.

Some of our information comes to us from medieval manuscripts, some from myth and legend, and some is plain speculation and conjecture. Now we are also able to explore our past scientifically, using advanced Y-Chromosome DNA testing.

After you have explored this project a bit, click on the "Join Request" tab at the top of the page. There are specific markers that would indicate links to the ancient Mag Uidhir clan. Because of this, the 67 marker test is required. Be sure to do this from the McOsker/McCusker Project site in order to properly join this project.

Remember that since the Y chromosome is passed from father to son, with very little changes over the generations, only males can take this test. Sorry ladies, but you must ask a male relative to join, preferably a father or brother.

See our family website for maps, historical documents, family tree information, blogs, etc at

You should also find that you would fit with various other projects. There is no additional charge for joining multiple projects! After you have received your initial Y-DNA test results, we will see if you may have additional opportunities. For example, the McOsker/McCusker Project Administrator is also currently a member of the Airghialla Mag Uidhir project at