This family is said to derive from LOGAN, or the Valiant (third son of O'Neal, monarch of Ireland, of the blood royal of Heremon), who fled his country in consequence of slaying, in single combat, about AD 595, his father's nephew, Coleman, King of Timoria, in Hibernia; and subsequently passing over into France, and marrying the daughter and heir of the Duke of Aquitaine, himself and his descendants became, for several generations, sovereign princes of that dukedom.
From these princes descended
SIR HENRY DE LEON (son of Thomas, Duke of Aquitaine), who was brought into England with his brother Thomas, when an infant, by HENRY II, the deposer of his father; and accompanying the Earl of Moreton (afterwards King JOHN) into Ireland, in 1185, obtained those extensive territorial grants in the counties of Longford and Westmeath then denominated Dillon's Country, but altered by statute, in the reign of HENRY VIII, to the Barony of Kilkenny West.
Sir Henry married a daughter of John de Courcy, Earl of Ulster, and was afterwards styled "Premier Dillon, Lord Drumraney".
From this feudal lord lineally sprang
GERALD DILLON, of Drumraney, County Westmeath, chief of the family of Dillon towards the end of the 14th century, left two sons, the elder of whom, SIR MAURICE, was ancestor of the Viscounts Dillon; and the younger, SIR JAMES, of the Earls of Roscommon.
Sixth in descent from Sir Maurice was
SIR THEOBALD DILLON, Knight, of Costello-Gallen, County Mayo, who was created VISCOUNT DILLON in 1622.
His lordship married Eleanor, daughter of Sir Edward Tuite, of Tuitestown, County Westmeath, and sister of William Tuite, of Tuitestown, County Westmeath.
He died at an advanced period of life, in 1624, leaving so numerous a progeny that he assembled, at one time, in his house at Killenfaghny, more than one hundred of his descendants.
He was succeeded by his grandson,
LUCAS, 2nd Viscount (1610-29), who wedded, in 1625, but when fifteen years of age, Lady Mary MacDonnell, second daughter of Randal, 1st Earl of Antrim; by whom he left at his decease an only son, his successor,
THEOBALD, 3rd Viscount (1629-30); who died in infancy, when the title reverted to his uncle,
THOMAS, 4th Viscount (1615-72), who espoused Frances, daughter of Nicholas White, of Leixlip; and was succeeded at his decease by his by his eldest surviving son,
THOMAS, 5th Viscount, who married Elizabeth, eldest daughter of Sir John Burke, Knight, of County Galway; but left no issue.
His lordship died in 1674, when the title reverted to his kinsman,
LUCAS, 6th Viscount, great-grandson of the 1st Viscount, being the eldest son of Theobald Dillon, third son of his lordship's eldest son, Sir Christopher Dillon, Knight.
This nobleman dying without issue, in 1682, the title devolved upon
THEOBALD DILLON, of Kilmore, as 7th Viscount (refer to Sir Lucas Dillon, 2nd son of 1st Viscount).
This nobleman, an officer in the army, attached himself to the falling fortunes of King JAMES II, and was outlawed in 1690.
His lordship wedded Mary, daughter of Sir Henry Talbot, of Templeoge, County Dublin, and had, with other issue,
HENRY, his successor;After the decease of his lordship, in 1691, the outlawry was reversed in favour of his son and successor,
Arthur, father of 10th and 11th Viscounts.
HENRY, 8th Viscount, who espoused Frances, second daughter of George, Count Hamilton, and was succeeded at his decease, in 1713, by his son,
RICHARD, 9th Viscount (1688-1737), who married Lady Bridget Burke, second daughter of John, 9th Earl of Clanricarde, by whom he left at his decease an only daughter, Frances, who wedded her first cousin, and his lordship's successor,
CHARLES, 10th Viscount (1701-41), who died without issue and was succeeded by his brother,
HENRY, 11th Viscount (1705-87), a colonel in the French service, who espoused, in 1744, Lady Charlotte Lee, eldest daughter of George Henry, 2nd Earl of Lichfield, of Ditchley Park, Oxfordshire, by whom he had issue,
CHARLES, his successor;His lordship was succeeded by his eldest son,
Arthur, a general in the French service;
Frances; Catherine; Laura; Charlotte.
CHARLES, 12th Viscount (1745-1813), who conformed to the established church in 1767, and claimed, and was allowed, the viscountcy, as 12th Viscount, by the Irish House of Lords in 1778.
His lordship married firstly, in 1776, Henrietta Maria Phipps, only daughter of Constantine, 1st Lord Mulgrave, by whom he had issue,
HENRY AUGUSTUS, his successor;His lordship wedded secondly, a French lady, and by her, who died in 1833, he had a daughter, Charlotte, married in 1813 to Lord Frederick Beauclerk.
He was succeeded by his son,
HENRY AUGUSTUS, 13th Viscount (1777-1832), who espoused, in 1807, Henrietta, eldest daughter of Dominick Geoffrey Browne MP, and had issue,
CHARLES HENRY, his successor;This nobleman, assuming the additional surname and arms of LEE, was succeeded by his eldest son,
Theobald Dominick Geoffrey;
Arthur Edmund Denis;
Henrietta Maria; Margaret Frances Florence;
Louisa Anne Rose; Helena Matilda.
CHARLES HENRY, 14th Viscount (1810-65).
- Charles Henry Dillon, 14th Viscount (1810–65);
- Arthur Edmund Denis Dillon, 16th Viscount (1812–92);
- Harold Arthur Dillon, 17th Viscount (1844–1932);
- Arthur Henry Dillon, 18th Viscount (1875–1934);
- Eric FitzGerald Dillon, 19th Viscount (1881–1946);
- Michael Eric Dillon, 20th Viscount (1911–79);
- Charles Henry Robert Dillon, 21st Viscount (1945–82);
- Henry Benedict Charles Dillon, 22nd Viscount (b 1973);The heir is his cousin, Thomas Arthur Lee Dillon (b 1983), the son of his uncle, the Hon Richard Arthur Louis Dillon (1948–2014).
Although Loughglynn is in County Roscommon, the vast majority of the Dillon estate straddled the border with County Mayo.
A third attic storey was built in the 1820s, though suffered a disastrous fire in 1904, when the top storey was not replaced, nor the end bays on the garden front which were reduced to a single storey.
There are ashlar limestone walls with quoins and a with roughly tooled limestone basement.
The entrance front has a pediment and a pedimented Doric doorcase.
In 1903, Loughglynn was sold to the RC Bishop of Elphin, who invited the Franciscan Missionaries of Mary to establish a convent.
The sisters established a dairy, and Loughglynn butter and cheese was famous all over the world until they ceased this activity in the 1960s.
They subsequently opened a nursing home.