In 1598, at the age of 18 Lettice FitzGerald married Sir Robert Digby, a Warwickshire landowner. Born in 1580, Lettice was the only child of Gerald FitzGerald, eldest son of the 11th Earl of Kildare. However, her father died around the time of her birth, leaving her, she would claim, as heir general to the great FitzGerald estates. Her cousin, who had become 14th Earl of Kildare, begged to differ and so in 1602 Lettice and her husband embarked on a long and costly law suit – the Jacobean equivalent of Jarndyce v Jarndyce – in pursuit of her entitlements. During the course of a legal battle that lasted almost two decades, they were able to prove that the will of Lettice’s grandfather had been fraudulently altered after his death in order to disinherit her, but still the fight continued. Eventually, in 1619 King James I, while rejecting Lettice’s claim to be the 11th Earl’s heir general, granted her and her heirs the manor of Geashill, comprising some 30,000 acres in King’s County (now Offaly), thereby partitioning the FitzGerald patrimony. The following year, the king recognised Lettice as Baroness Offaly for life, on the understanding that after her death the title would revert to the Earls of Kildare.

At the centre of the Geashill estate lay a castle, originally erected in the late 12th or early 13th century by Maurice FitzGerald, second Baron Offaly. For a considerable period during the Middle Ages, this property had been in the hands of the O’Dempsey clan, but was back under the control of the FitzGeralds by the time Lettice was born. It is here that she chose to live following the death of her husband, Sir Robert Digby, in 1618 and the confirmation by the crown of her right to the estate soon afterwards. By then in her early 60s, Lettice was in residence at Geashill Castle at the onset of the Confederate Wars in 1641 and that found herself besieged by the O’Dempseys, to whom she was related. They offered her and her family safe passage if the castle was surrendered, otherwise it would be burnt down. In the face of this threat, she replied ‘Being free from offending His Majesty, or doing wrong to any of you, I will live and die innocently, and will do my best to defend my own, leaving the issue to God.’ The siege was eventually lifted, but renewed the following spring when the attackers arrived with a make-shift cannon: it exploded at the first shot, as did a second attempt using the same device. Meanwhile, as Terry Clain notes in the Dictionary of Irish Biography, Lettice  ‘affected an aristocratic sang-froid in the face of imminent peril.’ Eventually, in October 1642 she was persuaded by allies to leave the property and subsequently retired to live on her late husband’s property in Warwickshire, where she died in 1658. Geashill Castle and the surrounding estate was inherited by her grandson, the second Baron Digby (her eldest son having predeceased her), whose heirs continued to own the property until the last century. 

At some date, perhaps as early as the 17th century, the Digbys built a new house to the immediate east of the old castle, part of which was most likely incorporated into the structure, where material from the abandoned building was probably also reused. The house appears to have been substantial but somewhat plain, of seven bays and two storeys, with a series of service extensions and yards further to the east. The south front had short projecting wings on either side of the central three bays creating a shallow forecourt. In 1860, Dublin architect James Rawson Carroll remodelled the house, adding a porch on the south side, a canted bay window on the ground floor of the north side and cambered arches over the windows on the west. The Digbys chose to live on their English estate, Sherborne Castle in Dorset, so the house at Geashill was occupied by a succession of agents who looked after the family’s Irish property; in the opening decades of the last century, the agent was Reginald Digby, a cousin of Lord Digby. In 1922, Mr Digby needed to go to London for an operation, but was unwilling to leave Geashill Castle unattended, aware that the place would be vulnerable to assault, this being at the height of the Civil War. However, eventually he was required to leave and on August 19th 1922, the building was attacked and burnt. Like other house owners whose property suffered in this way, the Digbys applied for compensation from the courts but because nobody was resident in Geashill Castle at the time, it was argued that the family was entitled to only minimal funding. In consequence, the house was not rebuilt but left as a ruin. Under the terms of the Wyndham Act of 1903, most of the ancient estate had already been sold to tenants and in 1926 the Land Commission took over the demesne, thereby ending a link with this part of the country that stretched back not just to plucky Lettice Digby in the 17th century but as far as the O’Dempseys in the 14th century.