Kingdom of Uí Failghe

The kingdom of Uí Fháilghe, Uí Failge (early spelling) or Uíbh Fhailí (modern spelling), (pronounced [iːvʲ ˈalʲiː]) was a Gaelic-Irish kingdom which existed to 1550, the name of which (though not the territory) is preserved in the name of County Offaly (Irish: Contae Uíbh Fhailí), Ireland.

It takes its name from the legendary king Rus Failge (fl. AD 507–514).

It successfully fought off encroachments by the Uí Néill, the Eóganachta, and the Normans however with loss of territories.

"The traditions of warfare in the fifth century between Ui Neill and Laigin in Brega and Mide ... [show] the Ui Failgi certainly suffered most material damage through the loss of territory in Offaly and Westmeath".

[2] O'Donovan cites O'Heerin as giving that Offaly was originally subdivided into seven cantreds: Tuath Geisille (Geashill); Hy-Regan (Tinahinch); Clann-Maoilughra (Upper Philipstown and Portnahinch); Clar Colgain (Lower Philipstown); Tuath-Maighe or Tethmoy (Coolestown and Warrenstown); Magh Aoife, or Fearann Uí Mhurcháin, (northern half of the Ophaley); Tuath Leighe (southern half of Ophaley).