One of the earliest known settlements in County Offaly is at Boora Bog which dates to the Mesolithic era. Excavations there provide evidence of a temporary settlement. Stone axes, arrowheads and blades were discovered which date to between 6,800 – 6,000 BCE.

The Kingdom of Uí Failghe from which the name Offaly is derived, was ruled by the Ó Conchobhair Failghe (anglicised as: O'Conor Faly) whose territory included the east of the county. The Kingdom of Firceall ruled by the O'Molloy clan constituted much of the center of the county. Much of the south of the present-day county was ruled by Ó Cearbhaill of Éile (anglicised as  O'Carroll Ely).

Uí Failghe was a petty kingdoms in Gaelic Ireland located just outside the English controlled area known as the Pale. When Mary Tudor succeeded to the English throne in 1553 she set about re-establishing English control of Ireland by ‘planting’ English…