The Fitzpatrick Y-DNA study has found there are several large and distinct groups of Fitzpatricks.
Aligning the results of the DNA study with historical records and genealogies has enabled some of these larger genetic groups to also be defined by geographic location. They are Fitzpatrick of Counties Tipperary, Kilkenny and Laois (FGC5494...A1488), Fitzpatrick of Bréifne (FGC11134...BY12234 and L513), MacGilpatrick of Iveagh and Newry Co. Down, Co. Kildare and Co. Louth (Z255...BY2849), O'Mulpatrick of Bréifne, and O'Mulpatrick of Mhumhain (FGC11134...CTS4466)
In addition to the larger groups mentioned, there are many smaller genetic groups that include haplotypes R-L513, R-M222, R-U106, I-M223 and J-M172. The L513 group is particularly interesting because it is strongly associated with the surname Maguire and, therefore, may represent descendants of Gilla Phádraig of Fermanagh of the Maguires.
And then there are many individuals with no close Y-DNA matches to any other Fitzpatricks; they include men identified by haplotypes R-Z253, R-CTS1751, D, E, I and Q-M242.