Baronies were created after the
Norman invasion of Ireland as subdivisions of counties and were used for administration. While baronies continue to be officially defined units, they are no longer used for many administrative purposes. They have been administratively obsolete since 1898. Nevertheless, they continue to be used in land registration and specification such as in planning permissions. In many cases, a barony corresponds to an earlier
Gaelic túath which had submitted to the Crown. This is true of Newcastle, which at the time of its creation, was part of the túath of
Ui Donnchad. The
Ui Donnchad, or sept the
Mac Giolla Mocholmog, was also home to Vikings of
Dublin (Dyflyn) who were allies and trading partners of the Chieftain Dermot Mac Giolla Mocholmog during the century period. Following the initial Hiberno-Norman policy of integration and assimilation, the descendants of this chief became the FitzDermots. Through grants and intermarriage, by the time of the
shiring of County Dublin, Newcastle-Lyons was raised to the status of an
Irish feudal barony. In 1627 a disputed claim to the barony led to tragedy when
Edmond Butler, 3rd/13th Baron Dunboyne killed his rival James Prendergast; James' brother Edmond was recognised as baron, but later forfeited. It eventually came into the Newcomen family who secured succession in the seventeenth century. The village and castle bawn was fortified with walls and multiple tower houses. It later became a
pocket borough until the Parliamentary Union of Dublin with Westminster in the United Kingdom of Great Britain and Ireland in 1801. After the Union, and the famine, the Barony like Dublin City and County went into a long period of economic and population decline. ==Civil parishes==