Ley was one of the 'Ten Civic Families', or Tribes, of Kilkenny - civic [or civil] is intended to mean English, which to the authorities, would have been synonymous with civilised - it is axiomatic that the native Irish were uncivilised.
Waterford and South East of Ireland Archaeological Society Journal, 1906, described the history of the family thus;
The Anglo-Irish (compare this with next sentence) family of De Ley, Lye or Lee, in Latin de Lega, is found in connection with Kilkenny City and its neighbourhood from an early date.
It would appear that the family name was originally pronounced Ly, which was afterwards changed to Lee, the anglicised form of the old Irish surname Ua Laoigh (or O'Laoi).
(This seems to contradict the opening sentence, although it is probably intended as an aside. The family is almost certainly of English origin.)
Thomas de Leye was one of the Jurors who 'extended' the Countess of Gloucester's manor of Palmerstown, beside Kilkenny, in 1307.
Walter fitz Richard 'de Lega' or 'de Leye' made over his stone house in High Street Kilkenny, at the corner of Walkin Street to William Utlawe, on 18 October 1305; and Margaret Whyte, widow of Richard Ley, granted the outbuildings, yard, and lands adjoining this house, in the High Street, to Robert Graunte and Mabina, his wife, on 12 March 1383.
(Journal of RHAAI, 1873, pp 532-30)
Nicholas Ley d. 1585
It appears from the will of Nicholas Ley, that two messuages (ie farms, inclusive of dwellings), in the town of Kilkenny, 60 acres in Kylmelag, and 40 acres in Fynell, in the County Kilkenny had belonged to the Leys. In 1382, William Ilger, lately deceased, was stated to have been seized, in fee, of these same farms, and in 1389, the King, by Faulk de la Freygne, committed to John Lye custody of said lands. (Patent Rolls)
The lands of 'Kylmelag', here mentioned, are identical with the present townlands of Middleknock and Quarryland close to the old church of Kilmologga in the parish of St John's and liberties of Kilkenny, and are found in the possession of the Leys in the 16th century and the first half of the 17th century.
The land in 'Fynell' which, probably, also had belonged to the Leys before they came into the possession of Ilger, may be identified with Leyrath, beside Fennell Hill (now Gazebo hill, or Altamount), in the immediate neighbourhood of the above-mentioned townlands of Middleknock and Quarryland.
In Irish Leyrath is called Raw-a-ly, Rath a' Liaidhe, that is, Ly's Rath or Ley's Rath.
Thomas Ley was a Burgess from 1472 to 1515.
John Leye was foreman of the Jury of the 'Commoners of the Towne of Kylkenny' in 1537.
Nicholas Ley was probably the first of the family to settle in Waterford. Part of his life, at least, was passed in Kilkenny, and his residence was situated near 'Trinity Lane leading from the King's Street (ie Parliament Street), to the Black Freres' (ie the Black Abbey).
Trinity Lane, now Abbey Street, comprises all of the laneway or thoroughfare from Parliament Street to the Black Abbey, lying without the old city wall, whose exact position is here marked by an archway, all that now remains of one of the gates of the city, frequently mentioned in ancient records as the 'Black freryn Gate' and the 'Inner Friern Gate'. The remaining portion of the laneway, viz., that which extends from Parliament Street to the old Gate is now known as Lee's lane. Nicholas Ley's house stood in Lee's Lane beside the gate.
Nicholas Ley was Sheriff of Waterford City in 1581. He died on 10 December 1585.
He had these children:
Walter, to whom he left the property in Kilkenny, apparently in the hope that he would return from Spain. He never did.
Thomas, who got Walter's property in Kilkenny. He was Sovereign of Kilkenny in 1609, and in the same year, became its first Mayor. (In the Genealogical Office, Ms 180, according to an undated will of Thomas Ley, Alderman, and seneschal of Bullyne, and Leynagh, Kilkenny, who married a Catherine Leonard, had a son, Nicholas, and daughters Margaret, Katherine, Mary, Lettice, and Maura(?). Nicholas, who died before his father, had married Mary Duffy, and they had a son, Thomas Ley, born 1613.) Thomas died 17 Feb 1629/30 and was succeeded by his 16½ year old grandson, Thomas Ley fitz Nicholas, who forfeited his property, as a papist, in Cromwell's confiscations, and was banished to Connaught in 1653. This latter Thomas was probably the father of Nicholas Ley fitz Thomas, of Kilkenny, who was married to Anne Langton by the Rev William Daton PP, St Mary's Kilkenny, in January 1681/2; Richard; James; Simon, of Waterford, merchant, whose will was proved 1602;
John, of Waterford who died in 1597, and with his wife, Helen Walsh, who died the same year, is buried in the Holy Ghost Friary Waterford; Marion; Kate; and Lettice.

According to a message on the Ancestry bulletin board for Ley a branch of the Ley family moved from Ireland to Belgium at that time (c.a 1540, Nicholas Ley). They stayed in Bruges until the French revolution in 1789 as "consul of the English nation". Then they fled to Germany where a part of the family is still established, but one branch came back to Belgium with King Leopold I in 1830. He was a Saxe Cobourg from Germany. The Ley family is established in Belgium since then.