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Guide to the records of the Ordnance Survey

The following guide draws on the archives of the Ordnance Survey held in the National Archives and aims to highlight the research potential of the collections of an agency which has been creating maps of the country since the early nineteenth century.


Since 1824 the Ordnance Survey has been concerned with making maps of Ireland. In the period between 1824 and the present day it has created very large quantities of archives, some of which have already been transferred to the National Archives. The archives transferred consist of part of the administrative archives, most of the archives generated by the mapping of the country at the scale of six inches to the mile (1:10560) and town plans at various scales.

The Ordnance Survey continues to hold a very large quantity of records which will be transferred to the National Archives over the next few years. These consist of administrative records and records created in the survey or making of other maps at various scales, including 1-inch and 25-inch maps.

The Ordnance Survey attached great importance to record keeping and most of the records of these enterprises have survived in fairly complete condition. The records consist of a wide variety of items in different formats, from engraved copper plates to manuscript coloured plans of towns, notebooks of theodolite observations, computations of the square area of each of the 60,000 townlands of Ireland, verbal descriptions of boundaries and name books which record evidence on the orthography of the place names. These archives do not contain material of interest for genealogical-type research, unless relating to persons employed by the Ordnance Survey. For general information about the history of ordnance mapping, the researcher should consult the following publications: J. H. Andrews, A Paper Landscape, Oxford, 1975 and J. H. Andrews, History in the Ordnance Map, 2nd ed. 1993 (published by David Archer, The Pentre, Kerry, Newtown, Montgomeryshire, Wales SY16 4PD).

Many of these archives are maps, while others are highly technical in nature, therefore work on preparing them for public inspection consequently is slow. The lists below are for those archives, the arrangement and listing of which are complete – further lists will be added as they are ready.

Arrangement of the archives

The Ordnance Survey had its own highly developed system of numbering and arranging the records of the six-inch survey, and this has largely been retained in the National Archives. The country was divided into five Districts (A, B, C, D and E), starting in the north and within each district civil parishes were numbered from 1. All of the records relating to a particular parish therefore bear the District letter and the parish number eg. C 5 is the parish of Burt, Co. Donegal. The Districts disregarded county boundaries. The same parish numbers were allocated in all five Districts so the District letter is an essential part of the unique reference number. This system was used by the Ordnance Survey until the publication of the maps, after which the county name and 6-inch sheet number became the reference.

Place names of parishes

The place names of parishes given in the lists are as they appear in the archives, and in some cases this can cause difficulties as the same names may have been standardised at a later stage with a slightly different spelling. A searchable index of standardised parish names, giving the county and reference number for each parish, is available online. It is useful for the researcher with an interest in a particular parish to find the parish name and reference number in this index, as this provides a means of checking which archives are extant for the parish.


The five districts did not follow county boundaries and as can be seen from the list below, some counties are in several districts.

  • Antrim – A, B, E
  • Armagh – A, D
  • Carlow – A
  • Cavan – A, B, E
  • Clare – B
  • Cork – A, B, C
  • Donegal – C
  • Down – A, E
  • Dublin – E
  • Fermanagh – B
  • Galway – B, C
  • Kerry – B
  • Kildare – A
  • Kilkenny – C
  • King's County – C
  • Leitrim – C
  • Limerick – B
  • Londonderry – B, C, D
  • Louth – E
  • Longford – C
  • Mayo – B
  • Meath – B, E
  • Monaghan – A, B
  • Queen's County – C
  • Roscommon – B, C
  • Sligo – B
  • Tipperary – C
  • Tyrone – A, B, C, D
  • Waterford – A
  • Westmeath – C
  • Wexford – A
  • Wicklow – A

Additional online resources: OS database