Dillon, Theobald (d. 1625?), 1st Viscount Dillon of Costello-Gallen, administrator and landowner, was the third son of Thomas Dillon of Ardnecragh in the barony of Kilkenny West, Co. Westmeath, and his wife Margery, daughter of Sir Christopher Dillon of Kilmore. His family was originally Anglo-Norman, but he grew up in a highly Gaelicised area on the outermost fringes of the Pale. However, a cadet branch, many members of which prospered by entering the royal government, had settled in the more anglicised Co. Meath. During the 1560s this branch succeeded in being appointed by the crown as seneschals of Kilkenny West, thereby enabling them to become effective leaders of the Dillon clan. This development may not have been entirely welcomed by Theobald's family. Nonetheless, the patronage of the Meath Dillons who were led by Sir Lucas Dillon (qv) greatly furthered Theobald's own career.
During his early adulthood, he resided in Dublin where he was a merchant up to about 1580. He also claimed to have entered the royal service in some capacity circa 1573. In 1578, he became involved in a long-running legal dispute with Turlough Carew who alleged that Dillon had seized his lands in Co. Meath by unfair means. Despite Carew's efforts, Dillon appears to have retained these lands. His success in this regard probably encouraged him to pursue a far more ambitious scheme. In summer 1580, he agreed to act as protector to Sean McCostello, a Gaelic lord who ruled the barony of Clan Costello on the eastern edge of Co. Mayo. In return, he received some land near Castlemore. The McCostellos were a weak clan and clearly felt threatened both by the crown's extension of its authority into north Connacht and the resulting increase in political and military instability in the region. As a result, Sean and his supporters made this unusual offer to Dillon who had both the knowledge and the personal connections to manipulate the machinery of the royal government on their behalf. His decision to accept can be seen as part of a general strategy undertaken by the Dillon family to advance their interests by acting as intermediaries between an expanding royal administration and various Gaelic clans. Lucas, Robert (qv) and Thomas Dillon all held high government office, all entered into similar arrangements with other Gaelic lords and all promoted Theobald's scheme to the government. However, Theobald's arrangement was by far the most radical, the most risky and potentially the most lucrative.
In moving to a remote and lawless part of the country, Dillon was encouraged by various royal officials who regarded this as a first step towards establishing a more sizeable English presence there. He went to London in summer 1580 and again in early 1582 to seek grants of land in Westmeath and Longford as a reward for his services, but does not appear to have been successful. His most important patrons were Francis Walsingham, who was the queen's chief adviser on Irish affairs, and Nicholas Malby (qv), governor of Connacht, who probably secured Dillon's appointment as sergeant at arms for Connacht and as general collector and receiver of the composition rent for the provinces of Connacht and Thomond in May 1582. The latter post entailed the collection of the tax that funded the royal army in Connacht, making him a key administrative figure in the province. It also involved some personal risk as was borne out in 1583 when Richard an Iarainn Burke (qv), lord of the MacWilliam Iochtar (Burkes of Mayo), and his wife Gráinne O'Malley (qv) tried to intimidate him with a show of force when he arrived to collect his composition rent. His role as local administrator allowed him to develop contacts throughout the province and as the 1580s progressed he began acting on behalf of the Burkes of Mayo, the MacGeoghegans of Westmeath, the O'Kellys of Galway, the O'Garas of Sligo and the O'Rourkes of Leitrim.
After Malby died in 1584, Richard Bingham (qv) became governor of Connacht. Initially Dillon got on well with him, but they became mortal enemies during 1585. Whereas Malby had shown considerable diplomatic finesse and guile in his dealings with the local Irish, Bingham rapidly alienated them with his harshness, brutality and personal acquisitiveness. Inevitably Dillon's alternate role as agent for the local Irish drew him into conflict with Bingham. In November 1585 he succeeded in having one of Bingham's subordinates Henry Ealand, sheriff of Roscommon, prosecuted in the court of castle chamber in Dublin for abuse of his position. This victory was due to the support of the lord deputy, Sir John Perrot (qv), who, disliking Bingham and eager to win the confidence of the natives, used Dillon to undermine Bingham in Connacht. Bingham intensified the bitterness between them by effectively dismissing Dillon as collector of the composition of Connacht (c. 1586). During summer 1586, the Mayo Burkes rebelled, having been encouraged to do so by Dillon who promised to procure their pardon. That autumn Perrot came to Connacht in an attempt to end the conflict peacefully and with Dillon's help investigated a number of complaints against Bingham. However, the rebel leaders, having been badly mauled by Bingham's forces, appear to have concluded that Dillon had manipulated them and in November revealed to the government that he had influenced their decision to rebel. On 20 February 1587 the case against Bingham came before the court of castle chamber, but Bingham was acquitted and Dillon reproached for making false and malicious accusations against him.
Despite this setback, he had prospered in his role in Connacht. During 1585–6 Sean McCostello's rule over his clan was threatened by a number of his relatives, some of whom had Bingham's backing. However, with Dillon's support, he prevailed. Doubtless considering himself beleaguered by threats, both internal and external, Sean accepted a renegotiation of the terms of his alliance with Dillon. In 1586, Dillon arranged for McCostello to surrender and be re-granted his lands by the crown. Having secured royal recognition of his lands, McCostello then transferred half of his holdings to Dillon who appears to have gone on to purchase more land in the barony. The McCostellos later complained that Dillon had exploited them, but for the moment regarded him as their protector. Previously, the barony of Clan Costello had been exempted from paying the composition rent, partly due to its poverty and partly to Dillon's influence. In 1587, he negotiated with royal officials on behalf of the freeholders of Clan Costello and secured a deal whereby less than a third of the barony paid the composition. Bingham protested bitterly but fruitlessly at this arrangement. In possession of a strong title to land in Mayo, Dillon settled his relatives from Westmeath there as tenants on his lands and appears to have established a flourishing colony. By his own reckoning, he enjoyed an income of 1,000 pounds a year. Certainly, he was wealthy enough to support a personal army of about 130 men, which he used to expand both his own power and that of the crown.
Politically, he lost influence in 1588 when Perrot was replaced by Sir William Fitzwilliam (qv) who disliked Dillon. About August 1588, at a time when the defeated Spanish Armada lay off the west coast of Ireland, Dillon detained Ealand who had been bringing an important message from Bingham to Fitzwilliam. For this, Fitzwilliam had imprisoned Dillon in Dublin castle by February 1589 and only the intervention of Walsingham secured his release before the end of April. By then a number of Gaelic clans in Connacht, but particularly the Burkes of Mayo, had become thoroughly alienated from the crown. Dillon could no longer function as an effective mediator and was seen primarily as an agent of the government. Moreover, with rebel Burkes raiding his lands, Dillon became an advocate of repressive measures in Connacht. Now having a common enemy, Dillon's relationship with Bingham improved greatly although there would always be friction between the two.
In 1590–91 court politics rudely interrupted more parochial concerns. A power struggle between Perrot and Fitzwilliam for control over Irish affairs had resulted in Perrot's arrest on a trumped up charge of treason. A number of Perrot's Irish clients were arrested and conveyed to the Tower of London, Dillon among them in August 1591. One of the charges against Perrot was of having encouraged Sir Brian O'Rourke (qv) into rebelling and it is likely that the interrogation Dillon was subjected to in September related to this. Following Perrot's conviction of treason, Dillon was released on 15 July 1592.
For the next four years, he was heavily involved in fighting the rebels in Connacht, assisting the royal forces with his own private army of about 130 composed of his tenants and relatives. On 18 August 1595, the government gave him command of a troop of 50 horse. Meanwhile, the rebels found a powerful ally in Red Hugh O'Donnell (qv), lord of Tyrconnell, and by the close of 1595 were set to sweep the crown's forces out of north Connacht. Aware that crown officials in Dublin and London were exasperated by this development, Dillon and a number of recently arrived landowners and military officials tried to cast all the blame for this on Bingham, accusing him of causing the uprising by his cruelty, and securing his dismissal in 1596. This did nothing to improve the crown's military position and by the end of 1596, Dillon and his extended kin had been forced to flee their lands in Mayo, which were overrun by rebel forces.
Undaunted, Dillon re-established himself further east in his native barony of Kilkenny West where he usurped the office of seneschal from James Dillon, son and heir to his former patron Lucas. Theobald effectively became a war lord in the area, expelling James's rent collector. The government tacitly accepted this development, recognising that Theobald was both better able and more motivated to carry the fight to the rebels. Squatting with his followers on the borders of Connacht he awaited his chance to regain his property. In fact, it was the rebels who came to him as the crown's position continued to deteriorate. The main rebel leader Hugh O'Neill (qv), earl of Tyrone, often dispatched reinforcements south from Ulster through Westmeath into Leinster and Munster to aid the rebels there. At times Dillon's forces were able to disrupt or impede their progress and capture rebel messengers. He also defended and provisioned the garrison at Athlone; his castle at Gallen on Lough Reagh in Co. Roscommon was an important royal base. Due to his past contacts and knowledge, he was regularly consulted by royal officials on Connacht affairs. On 27 July 1599 the lord lieutenant Robert Devereux (qv), 2nd earl of Essex, knighted him; that November, he accompanied Essex to England hoping to receive some financial compensation for his losses at the hands of the rebels. However, the queen was extremely angry with Essex for his inability to crush the rebellion in Ireland and for suddenly returning to England with many of his captains. As a result all Dillon gained from his audience with the queen was a royal rebuke and he returned chastened to Ireland in December.
Worse was to follow in late January 1600 when Tyrone marched into Kilkenny West with overwhelming force and invited Dillon to meet him. After taking the precaution of retiring to Athlone, Dillon wrote Tyrone a contemptuous refusal declaring his steadfast allegiance to the crown. The rebels promptly devastated Dillon's territory. Despite having his troop of horse disbanded and his personal income reduced to nothing, he continued to lead his followers in support of the crown. His relatives were involved in constant clashes with local rebels while he often participated in raids into Connacht. He dispatched a succession of letters to the queen's chief minister in London, Sir William Cecil, outlining how he and his followers had suffered at the hands of the rebels and appealing for some form of public income. When after 1599 the crown wrote off Connacht, maintaining a few token garrisons in a province largely under rebel control, Dillon bemoaned this strategy in his letters to Cecil. Also, he resented the manner in which many of his neighbours in Westmeath came to secret accommodations with the rebels leaving Dillon to bear the brunt of their assaults. Cecil disregarded his unsolicited and self-interested advice and ignored his appeals for support.
After the final suppression of Tyrone's rebellion in 1603, he was able to recover his estates in Mayo. As late as 1607, he was complaining that he was still struggling to attract tenants for his lands in Connacht. However, in time, he became one of the wealthiest landowners in Connacht, the bulk of his estates being in the barony of McCostello, but also holding land in Roscommon and Westmeath, where he resided at Killefaghny. After 1603, he kept a low profile and did not, unlike many other catholic landowners, openly associate himself with the constitutional opposition to the royal government. In March 1622, he was created Viscount Dillon of Costello-Gallen, having paid 2,500 pounds for the honour, an indication of his enormous wealth. His death is normally described as occurring on 15 March 1624 at his home at Killefaghny, Co. Westmeath, but official correspondence regarding a legal dispute he was involved in indicates that he was still alive in June 1624. The use of the 1624 death date may reflect confusion over the new and old style calendars and his death probably took place on 15 March 1625.
He married Eleanor, daughter of William Tuite of Tuitestown, Co. Westmeath. They had seven sons and five daughters. He was succeeded by his grandson Lucas. Two of his sons became Franciscan priests and two of his daughters Eleanor Mary Dillon (qv) and Cicely Dillon (qv) became nuns and founded the Poor Clare movement in Ireland. His second son Sir Lucas (qv) was a prominent member of the catholic confederation of Ireland during the 1640s and another son James (qv) enjoyed a distinguished military career in the army of the catholic confederacy and in the French army.