The history of the Ordnance Survey in Ireland

The Ordnance Survey Office in Ireland was established in 1824. The Office was initially part of the British army under the Ministry of Defence.

The Ordnance Survey Office was created to carry out a survey of the entire island of Ireland, for the purpose of updating land valuations for land taxation purposes. The original survey at a scale of 6 inches to 1 mile was completed in 1846 under the direction of Major General Thomas Colby. Ireland thus became the first country in the world to be entirely mapped at such a detailed scale.

In the course of surveying the country, the staff of the Office were responsible for a number of advances in surveying practice. These ranged from Drummond’s limelight to Colby’s Bar – the bimetallic parallel bars used to measure distance to a previously unattainable level of accuracy. The drive to improve technical capability has continued to remain a core value in ordnance survey work to the present day.

The Ordnance Survey Office was based in Mountjoy House in Phoenix Park, Dublin. Mountjoy House was originally built in 1728; it had housed the mounted escort of the Lord Lieutenant who resided in the nearby Vice-Regal Lodge (now Áras an Uachtaráin). Mountjoy House and its surrounding buildings still serve as our headquarters today.

The Office continued to operate as an agency of the British Ministry of Defence for 100 years until 1924 and the establishment of the new Irish Free State, when responsibility for it was transferred to the Irish Government’s Department of Finance. All staff employed by the Ordnance Survey Office were recruited through military channels until the 1970s, when the first civilian employees were recruited. The first female staff joined too at this time.

Ordnance Survey in Ireland was introduced as a State Body under the Ordnance Survey Ireland Act 2001. Under this Act, Ordnance Survey Ireland continued its mainstream public service function of creating and maintaining the definitive mapping records of the State and also assumed a new, more commercial function assigned to it under the Act of developing its commercial business and sales revenues.

In 2023, Ordnance Survey Ireland, along with the Property Registration Authority of Ireland and the Valuation Office, merged into the newly created state body Tailte Éireann under the Department of Housing, Local Government and Heritage, a department of the Government of Ireland.