John O’Donovan’s Ordnance Survey Letters of Kings County, 1837 – 1838: Scientific Survey, Clan Maliere and Placenames. By John Dolan

Ordnance Survey of Ireland 1824 – 1842

Townlands are the smallest official unit of administration in Ireland, followed by the Parish.  Our townlands are ancient divisions and some have existed under other names since pre-Christian times.

By the early 1800s, local taxes were based on the valuation of townland units. These valuations were based on hopelessly obsolete information and poor mapping, and it was necessary for the boundaries of townlands to be mapped accurately in order to provide a framework for new valuations. There are 64,642 townlands in the Republic of Ireland, with over 1,000 in Offaly.

The Duke of Wellington authorised a survey of Ireland in 1824 in response to requests from his brother, the Marquess of Wellesley, who was Lord Lieutenant of Ireland at the time. The task was given to Lt Col Thomas Colby and officers and sappers of the Royal Engineers with civil assistants. First established as a military office, all the staff were military employees until the 1970s, when recruiting of civilians started.

It was decided to carry out an experimental triangulation survey in 1824, using Ireland as a test area. When completed the Irish survey would be a model for Great Britain and other areas of the Empire. The aim of the survey was to standardise and anglicise the representation of the Irish landscape. Ireland was divided into a network of large interconnected triangles, mostly from mountain to mountain. Colby began by training a team of surveyors on how use very precise methodology. He chose the largest, most accurate optical surveying instruments. One such instrument was the theodolite, a precision instrument used for establishing angles. By knowing the triangle’s angles, you can calculate the length of the triangle’s three sides. All of the angles of the triangles were measured using the theodolite. Precision measuring chains were used between stations, facilitating the subdivision of the triangle for a detailed survey of every road and track, wall and hedge, river and stream, house and building. Observations were made at night as a rule, using a limelight, which is a bright luminescent light created from burning a block of lime in a hot hydrogen-oxygen flame. Over 2000 workers were employed on the Irish survey at its peak, the majority were locally recruited civilians but they were under military supervision. 

Thomas Colby              The Great Theodlite

Colby assigned Lt. Thomas Larcom to manage the effort to investigate and anglicise Gaelic placenames, Larcom recruited George Petrie to manage the office at Mountjoy Barracks and set up a team there.

Colby’s instructions were so detailed that every aspect of the work was covered, as there had never been any previous precedents for this type of work.  Field operations were completed in 1841– 2, the engraving and publication of the 6” maps were completed late in 1846 on a county basis. The maps were set to the standard of 6” to 1 English mile. When Colby moved into a house owned by Luke Gardiner it was renamed Mountjoy Barracks and is still the Ordnance Survey in the Phoenix Park today. The first edition of the Offaly maps were printed in 1838, the second edition in 1884-1885 and the third edition in 1911-1913.

Birr, First Edition OSI Map 1834

Birr, First Edition OSI map, 1838

Ferbane, First Colour Edition OSI Map

Ferbane, First Colour edition OSI map

Tullamore, Final Edition OSI Map 1911

Tullamore, Final Edition OSI map 1911


Surveyor's CampPicture of Surveyors’ Camp


John O’Donovan (1806 – 1861)

O’Donovan was born at Attatteemore, Co Kilkenny. He was educated at Hunt’s Academy in Waterford. He went to Dublin in 1823 to study and copy manuscripts. In 1827 he was employed by antiquarian James Hardiman, researching state papers and traditional sources in the Public Records Commission.

He then moved to Dublin to continue to study manuscripts. In Dublin he was engaged to teach Irish to Lt. Thomas Larcom in 1828. Larcom understood the importance of names on maps embracing all aspects of local information. At the same time, O’Donovan worked for Myles John O’Riley who collected early Irish manuscripts. In October 1830 Donovan joined the staff of the Ordnance Survey Department working under George Petrie and alongside Eugene O’Curry. As part of his work O’Donovan regularly travelled across the island gathering information about placenames although he was never in great health. He also researched maps and manuscripts in many archives in Ireland and in the UK in order to collect the original names for the 64,000 townlands. O’Donovan continued to work in the Placename Survey unit until 1842. 

He was a prolific writer and publisher with a deep knowledge of the earlier forms of Gaelic. In later life he prepared editions of Irish manuscripts to be translated into English, notably the Annals of the Four Masters. Also, in 1849 he became Professor of Celtic Languages at the newly founded Queens University, Belfast. 

O’Donovan had two aims for his field research, fulfil the aims of the Survey project by researching the backgrounds of the names of places, fields, rivers, mountains etc.  Secondly, a less official research into the ancient names of the Celtic Tuatha and map their extents. He also recorded local genealogies and traditions, particularly religious celebrations encountered in his travels.

He wrote his letters with a quill pen, often on paper of poor quality with his own style for punctuation. Sometimes he wrote placenames phonetically, often adding Latin phrases into the text. He also used the older Irish alphabet when adding quotes from old manuscripts.

John O’Donovan                   Older Irish Alphabet


Lt Col Thomas Colby issued detailed instructions on the treatment of place names, the correct orthography of the names of places were to be entered into a Name Book in the way it was locally spelt and the various modern modes of spelling it to be inserted in a second column.

The vast majority of names originated in the Irish language, placename spellings were drawn from a wide variety of manuscripts, particularly those of earlier written sources. These sources, written in Irish and Latin dated from 11th to 19th centuries. In addition, many documents already existed with Irish names in anglicised versions only. These would include the Rolls and Deeds, Inquisitions and Surveys, Deeds and Estate Maps, etc. The Book of Ballymote and Book of Lecan would be searched for genealogies. Castles owned by the Gaelic families also indicated the extent of their territories.

Kings County (December 1837 – February 1838)

O’Donovan’s first letter from Offaly is dated 18th December 1837 from Portarlington.  He was accompanied by Thomas O’Connor and they covered the county between them.  An example to illustrate the placename problems he would have been confronted with were the conflicting spellings of the county name – Offalie, Ophaly, Faly, Ofalia, Ophally or Ui Failghe!

In addition, he was to suffer from ill health over this period and the continuous bad weather did not help. On 18th December he writes ‘we are suffering most awfully from the weather, but no matter’. Bad weather continued to chase him to Banagher where he writes that the weather had assumed ‘a fierce and terrible aspect’.  By 18th January 1838 he was reporting snow to the depth of eight inches.

He was in poor health between January 24th to February 4th where he reports ‘O’Connor is working very well but I, unfortunately, are in the hands of the Doctor, and I’m not able to venture out. I have absorbed too much moisture.’

Before joining the Ordnance Survey, he had already established contacts in the county. He had spent long periods in the house of his patron Myles John O’Reilly at Heath House near Portarlington, so the district around was well known to him.  When in Banagher he linked up with his friend Mr. Richard Monck who ‘was the first who taught me Irish’.  Monck was a regular correspondent with O’Donovan and was at the time the assistant master at the Banagher Royal School.

However, while visiting Birr he declined to visit local historian T. L. Cooke. O’Donovan’s view was clear and pointed – ‘Mr. Cooke is an attorney at present living in Birr, but I do not like to call upon him, as I was told he was one of those self-sufficient people who wishes to be considered the only antiquarian oracle now living. A friend of mine called upon him to see if he could or would give me any information, but (he said that) he was already communicating with Lt. Wilkinson all he knows about the neighbourhood’! He finishes this letter of 24th January 1838 with ‘I am anxious to hear how I stand with respect to car hire (pony and trap); the expenses of this town are more than we can bear’.  Getting your travel expenses paid was a regular problem for the teams in the field.

There are two sections where O’Donovan spent considerable time researching and returned to on a number of occasions. The first one relates to the killing of Hugh de Lacy in Durrow and the difficulties he encountered in translating many of the early documentary accounts on the killing. The second was where he spent considerable time investigating Clonmacnoise. More of this in part 2.

O’Donovan arrived in Portarlington on 18 December 1837. His first task was to identify the extent of Clanmaliere, the lands of the O’Dempsys. The following illustrates the approach that he took with this and later Gaelic territories in Offaly and how he resolved various conflicts. His initial research was in the lands of Lord O’Dempsy, Viscount Clanmaliere. This took O’Donovan to the village of Clonygowan on the basis of an entry in the Annals of the Four Masters for 1576 ‘Owney, the son of Hugh O’Dempsy was treacherously slain in his own residence of Cluain na ngamhan’. He then examined a description of the extents of Clanmaliere by the Abbe Mageoghan which he found to be mostly inaccurate. Finally, he examined the 1556 Act of Parliament that formed ‘Leix and Ophaly’ to see if the boundaries of Clanmaliere could be identified. Then, he drew a map, see below, that defined the territories of the O’Dempsy. Note the names in Irish for Monasterevin, the castle guarding the river at Monasterevin, Clonygowan and the Sliabh Blooms.

Clan Malure the Country of the O'DempsyMap of O’Dempsey Country

On 22 December 1837 O’Donovan headed north from Portarlington and came across an ancient church site at Clonsast. The founding saint was St Brachan whose memory was celebrated on 3 December every year at his holy well Tobar-Brachain where the locals used to leave rags on the nearby bushes. A local pattern was held there annually in the field beside the well but it was abolished by the local clergy ‘due to the bad effects of whiskey’.

O’Donovan spent Christmas Day with Laurence Byrne at Fallybed near Athy.  He left Portarlington on 27th December for Tullamore via Mountmellick.  Here he confirmed the Irish spellings of many locations in the neighbourhood.

Killeigh was visited on 28th December 1837. There are five Killeighs (Cill Achaidh) in Ireland, two in Kilkenny, one each in Tipperary, Kerry and Offaly. O’Donovan identifies Cill-achad Droma Fada (the Church of the Field of the Long Ridge) from the Annals as the proper name for this Killeigh. The Placenames Database of Ireland is held by the Placenames Branch (Department of Culture, Heritage and the Gaeltacht) that holds the data, archival records and placenames research conducted by the State. Killeigh has 121 names in the database spanning from the 10th century through to 1837. Here are some examples:

Year                      Name

541                       Cill Achaidh Drumfhada

871                       ab Cill Achaidh

1401                     Killechi

1429                     Killeydh

1466                     Kylithe

1550                     Glaishestradnecleraghe

O’Donovan then delves into the background of the monastery and nunnery before visiting the cemetery near the Protestant church.  Here he records the names of the local families, some from outside the townland. They included the O’Duns, the tomb of O’Connor Faly, the O’Connor of Mount Pleasant, the tomb of Maxmilian O’Dempsy, Lord of Clanmaliere, and the resting place of John Molloy of the O’Molloys,

From Tullamore Thomas O’Connor on 1st January 1838 visited Monasteroris and Edenderry. O’Connor suggests that the original name for Edenderry was Ardanderry, the Front, or Face of the Wood.  However, the Placenames Branch database shows that there are also three references to Edenderry in Co Down, two each in Armagh and one each in Antrim, Tyrone, Armagh and Offaly. The Offaly reference in has 46 different spellings for the name from 1416 to 1837. Here are some examples:

Year                      Name

1416                     Etain Daire

1550                     Skeaghenuye

1563                     Ballyntogher

1603                     Edenderrie

1660                     Ballywilliam

1783                     Edenderry

Offaly History notes: John Dolan will continue his exploration of the work of John O’Donovan with a further piece featuring Banagher, Clonmacnoise and Durrow. In the meantime, readers might be interested in the following publications on the letters of John O’Donovan available from

Ordnance Survey Letters Offaly, ed. Michael Herity
Offaly Heritage 7 features the article ‘The Ordnance Survey letters of King’s County: their place in the historical literature of the
county’ by Michael Byrne


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