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Reilly Family History Notes

Michael R. Reilly

Last Updated: 06/06/2010

O'Reilly Castle


Lough Sheelin is over 7kms long, more than 3kms wide and covers an area of 1800 hectares and borders three counties, Cavan, Meath and Westmeath. Lough Sheelin, from the words She Linn, meaning fairy pool, originates as legend has it from a fairy well, and was used by a village as its water supply. However, there was a restriction on the use of the well. The lid had to be replaced every time water was drawn from it. Nevertheless one day, a woman neglected to replace the lid and the waters rushed out, drowned the entire village and thus created the lake, writes Geraldine Lynch.

Lough Sheelin is placed by ancient Irish sources in Cairbe Ui Gaibre which was a pre-Norman principality centered around Granard in Co. Longford. The largest island in the lake, Church Island has the remains of an early Christian oratory dating from the 400s. The island was then called Inis Oughter (upper island). In the late medieval period the lake was closely associated with the O’Reilly family. Crover Castle, which is built on a small island in the lake was reputedly erected by Thomas O’Reilly in the late 14th century. Thomas O’Reilly was the grandson of Giolla Iosa Rua, and pushed O’Reilly power into modern Co Meath. The castle is not far from the shore of Lough Sheelin and in the later Middle Ages the lake was seen as the border between the Irish and the English, the Anglo-Normans and the O’Reilly family. The village of the Mountnugent originally known as Daly’s Bridge in honor of the local landlord was on the border between the two.

In the late 1300’s the O’Reillys moved the seat of their power to Tullymongan above Cavan town. As the O’Reilly clan were in the fortunate position to occupy the border between the Gaels and the Normans they were in a unique position to exploit all the advantages that living on the border provided. However, by the late 1500s the Tudor state was extending its power throughout Ireland. The border region of Breffni was among the first to feel the pressure, with the Anglo Norman Nugents and Plunketts from Meath beginning to assert their power in Breffni on behalf of the English crown, and as the century progressed the pressure became greater. In 1566 the O’Reilly family were compelled to sign the Treaty of Lough Sheelin with the Earl of Sussex. By 1584 Breffni was shired and became the county of Cavan. The O’Reilly power finally collapsed in the wake of the Nine Year War (1594-1603). In 1601 Edmund O’Reilly (of Kilnacrott) was killed in Cavan. He was the last of the family to hold the title “The O’Ragahallie’.

To the south of Lough Sheelin, the lake borders Westmeath with the River Inny, linking Lough Sheelin to Lough Derravaragh. Finea, (Fiodh an Atha) is located to the south of the lake, and its literal translation from Irish means ‘words of the lord’ or ‘field surrounded by trees’. Finea was an important tactical point in the the Middle Ages between Navan, Meath and Longford. Lough Sheelin and Lough Derravaragh and the boglands that lay between them formed the ends of an impregnable defence line and were an impassable wilderness. Any army faced with this had either to go around on go through Finea and control of Finea was the key to controlling a good portion of South Cavan.

Ross Castle on the eastern side of the lake, was built in the sixteenth century. The tower of Ross Castle was used by Myles O’Reilly. Myles O’Reilly also known as Myles the Slasher was a cavalry officer in the 12 year war (1641-1653). A plaque in the hall of Ross Castle is inscribed
“This ancient castle in which the celebrated Myles O’Reilly, known as The Slasher in 1644 past the night previous to the Battle of Feinna at which he was killed, haven fallen into ruin was partly restored by his lineal descendant Anna Marie Maria Dease O’Reilly in 1864.”


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