Ó Treasaigh - anglicised Treacy, Tracey and Tracy, and earlier as (O) Trassy & c., the name probably meaning 'fighter, warlike, fierce'.
There are at least four distinct septs of this name recorded in the ancient sources: of south-east Galway who, though dispersed in early times, are still represented in their ancient territory; of County Cork and Limerick, with connections to the royal house of Munster (MacLysaght, 'Irish Families Series' 1980s eds); of County Leix, Slievemargy Barony, where they were lords of the Uí Bairrche. Connelath McTressy, Crayn McTressy, Euercath McTressy and Mardauth McTressy occur in the 'Red Book of Ormond' in 1304, as located in Cloncurry Co Kildare. De Bhulbh in 'Sloinnte na h-Eireann', (2000) says there was a sept in Co Fermanagh.
Many Treacys etc appear in the Tudor 'Fiants', usually recipients of 'pardons', e.g. RoryTrassy of Co Kildare in 1548, Rory O Trasse of Wicklow in 1564, Teige O Trassye of Laois in 1573, Wm O Treasie of Co Galway in 1585.
By the time of Sir William Petty's '1659 Census', Ó Treasaigh is found in the following counties, except noticeably for Cos Cork and Leix where there are none; (returns for Co Galway are missing): in Co Limerick they are in Small County Barony - O Trassy, 9 families; in Co Tipperary, Slieveardagh Barony - Trassy, 12 families, and in Eliogarty and Ikerrin - Trassy, 22 families; in Co Kildare, Salt Barony - Tressy, 7 families; in Co Kilkenny, Gowran Barony - Tressy, 8 families; in Co Fermanagh, Dunmully Parish - O Tressy, 7 families.
By the mid 19th century, and Griffith's 'Primary Valuation', the surname had settled into three forms Tracy (686 households) Tracey (350 households) Treacy (94 households). Most Tracys were in Tipperary (184 households) and Limerick (57 families) Traceys in Galway (38 families) and Tipperary (35 families) and Treacy in Galway (24 families).
In R.E. Matheson's 'Special Report on Surnames...in Ireland' (1894 & 1909) based on the birth registrations of 1890, Tracey and Tracy occur mostly in Co Dublin, and Treacy in Cos Tipperary and Galway
De Bhulbh states that the form Treacy is now 'very numerous' in Ireland, followed by Tracey, 'numerous'.
Tracy is also a Devonshire surname. and that of the Barons Sudeley, who derive their name from a place called Tracy in Normandy. This name was also carried to Ireland by Anglo-Irish Tracys in Co. Limerick: see baronets, Viscounts Rathcoole & c. Some numerous Irish surnames are identical in their anglicised form to British names, borne occasionally by 17th century English officials, settlers etc in Ireland. (v. Appendix). This does not alter the majority Gaelic provenance of these names. The 'Treacy' spelling, however, would be almost exclusively Irish.
Three famous bearers:
Nathaniel Tracy (1751-1796) American, son of an Irish-born father, big financial backer of the American Revolution.
Seán Treacy (1895-1920) of Soloheadbeg, Co Tipperary, hero of the Irish War of Independence 1920-21. Along with Dan Breen, he took part in the first action, an ambush of Crown Forces near to his home.
Spencer Tracy (1900-1967) Great Irish-American actor. Making a name first on Broadway, he starred in many Hollywood classics, such as 'Captains Courageous' (1937), 'Mannequin' (1937: with the great Joan Crawford) and 'Boys' Town' (1938). Two of these films earned Tracy an Oscar for best actor. In fact, he held the record, along with Olivier, for the most nominations. In 1940 Tracy was voted the nation's favorite movie actor in the magazine 'Fortune'. 'The Last Hurrah' (1958) is one of my own favorites, in which Tracy takes the role of an Irish-American mayor seeking re-election; he was chosen as 'Best Actor of the Year' by the National Board of Review, for that year. Perhaps one of his most memorable latter-day performances was in the film 'Judgement at Nuremburg' in 1961.
Also q. v. v. Boland, Boyle, Brady, Breen, Buckley, Canny, Car(e)y, Conway, Craven, Crowley, Cullen, Curry, Delan(e)y, Farren, Fearon, Foley, Gavin, Geary, Gorman, Hanl(e)y, Healy, Hurl(e)y, Hynes, Kelly, Kenny, Larkin, Loftus, Long, Luc(e)y, Lyons, Mullen, Rea, Reaney, Ring, Sexton, Trac(e)y, Tunney et. al.
884 AD Treasach, son of Becan, chief of Ui Bairche Maighe, was slain by Aedh, son of Ilguine. Of him Flann, son of Lonan, said:
'A heavy mist upon the province of Breasal, since they slew at the fortaliced Liphe, Heavy the groans of Assal, for grief at the loss of Treasach. Wearied my mind, moist my countenance, since Treasach lies in death. The moan of Oenach Lifi all, and of Leinster to the sea, is the son of Becan.'
The first reference to the name was in 1008 AD where it states "Gussan, son of Ua Treassach, lord of Ui-Bairrche, died".
The earliest reference to a Tracy in America was in 1653.
Many thanks to Declan Tracey from www.TraceyClann.com for this information