In 1426 the sixth Earl of Kildare enlarged and rebuilt the castle. In the latter half of the fifteenth century, Maynooth Castle became the centre of the Geraldine powerbase, as the Earls of Kildare increased their strength of ‘rule’. This was something which the English monarchy disliked. The culmination of the developing friction between the Fitzgeralds and the monarchy was the rebellion of Silken Thomas (so called because of his fine clothes).
Silken Thomas alias Lord Offaly was a son of Garret Óg, the ninth
Earl of Kildare. Thomas rose up in rebellion against the king who had
arrested his father, and held him in the Tower of London. Thomas marched
to Dublin Castle and threw down the sword of state, declaring himself
an enemy of the king. However, his rebellion was curbed when he and his
followers were defeated and the stronghold of Maynooth taken by the
English. All those within the castle were put to death and this became
known, ironically, as the ‘Maynooth Pardon’. Thomas, along with five of
his uncles, was later executed in London. Maynooth Castle then became a
royal castle and a popular residence for the Lord Deputies of Ireland.By
the seventeenth century however, the castle had fallen derelict. It
became the property of the Duke of Leinster and today only the ruined
keep and the gate-house survive.