There have been two creations of the title Baron Offaly, both in the Peerage of Ireland.
Two earlier medieval creations as Baron of Offaly existed for an earlier FitzGerald, who owned land in County Kildare, Ireland, including what was then "Offelan", a word that derived from the Irish Uí Faelain and not from what is now County Offaly. The original grant of the lordship of Offelan was in 1175 to Maurice FitzGerald, one of Strongbow's main supporters.
The first modern creation by Queen Mary I was for Gerald FitzGerald on 13 May 1554, who was also created Earl of Kildare at the same time and later restored to the senior earldom of Kildare (forfeit by his half-brother, Thomas) in 1569. The title (as well as the second creation of the earldom), became extinct in 1599 when the 13th earl's branch of the family became extinct and the senior earldom passed to his cousin, Gerald.
The second creation of the title was for Lettice Digby on 29 July 1620. She was the daughter of Gerald FitzGerald, Lord Offally (1559–1580; the eldest son of the 11th earl, who predeceased his father) and the wife of Sir Robert Digby. Her eldest son, Robert, was created Baron Digby on the same day. The patent of the barony stipulated that it was not to pass to Lord Digby, but instead to the head of the House of Kildare, who, at the time of Baroness Offaly's death in 1658, was George FitzGerald, 16th Earl of Kildare. The 20th earl was later created Duke of Leinster in 1766 and the dukedom and barony remain united.
FitzGerald Barons of Offaly
- Gerald FitzMaurice, 1st Lord of Offaly (c. 1152 – c. 1203)
- Maurice FitzGerald, 2nd Lord of Offaly (1190–1257)
- Maurice FitzGerald, 3rd Lord of Offaly (1238–1286)
- John FitzThomas FitzGerald, 4th Lord of Offaly, (1287-1316).
O'Conor Faly Barons of Offaly
- Brian O'Conor Faly (1525–1556) (In Irish, Brian mac Cathaoir O Conchobhair Failghe) attainted in 1550
Barons Offaly, first creation (1554–1599)
- Gerald FitzGerald, 11th Earl of Kildare, 1st Baron Offaly (1525–1585)
- Henry FitzGerald, 12th Earl of Kildare, 2nd Baron Offaly (1562–1597)
- William FitzGerald, 13th Earl of Kildare, 3rd Baron Offaly (died 1599)
Barons Offaly, second creation (1620–present)
- Lettice Digby, 1st Baroness Offaly (c. 1578–1658)
- George FitzGerald, 16th Earl of Kildare, 2nd Baron Offaly (1612–1660)
for further Barons Offaly, see Duke of Leinster
- Cokayne, George Edward, ed. (1895). Complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct or dormant (N to R). 6 (1st ed.). London: George Bell & Sons. p. 113. Retrieved 27 December 2011.
- Cokayne, George Edward, ed. (1890). Complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct or dormant (D to F). 3 (1st ed.). London: George Bell & Sons. p. 358. Retrieved 27 December 2011.
- Note on earlier barony and "Offelan" by Goddard Henry Orpen. Offelan was also sometimes spelt Ophelan. The Uí Faelain were a branch of the former Gaelic-era Leinster dynasty
- Journal of the Co. Kildare Archaeological Soc, 1893, p.186 Online version here
- Note on the O Conor Faly barony (published in 1914)
- Lundy, Darryl. "p. 15487 § 154864". The Peerage.[unreliable source]
- Cokayne, George Edward, ed. (1892). Complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct or dormant (G to K). 4 (1st ed.). London: George Bell & Sons. p. 368.