[1] Geashill barony is located in central County Offalysouth of the Grand Canal.

Geashill is roughly formed from the ancient Túath Géisille of the Uí Failge septs of Leinster.

As Viscount Clanmalier the Ó Diummasach (O'Dempsey) held part of this barony, where the main castle of the clan was located.

The Ó hAimherigin (O'Bergin) sept are noted as chiefs in this barony in medieval times.

This article related to the geography of County Offaly, Ireland is a stub.