Mac Giolla Phádraig Dál gCais ~ Fitzpatrick of the tribe of Cas

Clan Mac Giolla Phádraig Dál gCais is defined by their ancient possessions in County Clare, which included lands known as 'Ballyclenymacgilpatrick', i.e., the town of Clan Mac Giolla Phádraig.

The Mac Giolla Phádraig are also Dalcassian on a genetic basis, since they share common ancestry with Brian Bóruma, High King of Ireland, through their direct paternal line. 

In the sixteenth century, the clan held extensive land in west County Clare, but with the capitulation of the O'Briens, their territories were mostly lost. Nevertheless, some clan lineages established themselves anew on the Aran Islands and in Galway town, and – one way or another – there were further relocations to County Mayo and County Roscommon.

Of great interest are the more ancient origins of the clan, which can be traced back to descent from Scanlan Mac Giolla Phádraig of Upper Ossory, ca. 1150 AD.