The division into counties based on the model used in the English system, was introduced gradually by English settlers from the late 12th century onwards. These land divisions were formed following the Norman invasion of Ireland in imitation of the counties then in use as units of local government in the Kingdom of England. The older term "shire" was historically equivalent to "county". The principal function of the county was to impose royal control in the areas of taxation, security and the administration of justice at local level. Following a survey under the 1825 Boundary Survey Act, an extensive series of maps of Ireland was created by the Irish division of the Ordnance Survey for taxation purposes. These maps both documented and standardised the boundaries of the thirty two counties of Ireland.

County boundary dataset generated from the 2019 OSi National Statutory Boundary dataset. Ungeneralised.

Coordinate Reference System: Irish Transverse Mercator.