County Westmeath: History
Following the Norman invasion of Ireland, the territory of the Gaelic Kingdom of Meath formed the basis for the Anglo-Norman Lordship of Meath granted by King Henry II of England to Hugh de Lacy in 1172. Following the failure of de Lacy's male heirs in 1241, the Lordship was split between two great-granddaughters. One moiety, a central eastern portion, was awarded to Maud (de Geneville) as the liberty of Trim; the other moiety, comprising north-eastern and western portions, went to Maud's sister Margery (de Verdun) and in 1297 became the royal county of Meath. The liberty and royal county were merged in 1461. While the east of the county was in the English Pale, the west was Gaelicised in the fourteenth century and outside the control of the sheriff of Meath.
As a part of the better administration of the newly established Kingdom of Ireland, the Parliament of Ireland passed the Counties of Meath and Westmeath Act 1543, the eastern portion retaining the name Meath and the western portion called Westmeath.