Cook (Cooke), John (c.1609–1660), lawyer and regicide, was son of Isaac Cook(e), of Burbage, Leicestershire, England. He is identified conjecturally with ‘John Cook, esquire’ admitted into the King's Inns, Dublin, on 6 November 1634. This would be consistent with what was said later about his connection with the recently arrived lord lieutenant, Thomas Wentworth (qv). He may also have been the same Cook recorded as a counsel practising in the Irish court of chancery from 1634. One task with which Wentworth entrusted him was supervising the publication of the Irish statutes. A hostile commentator alleged that he absconded with some of the money to the Continent. Cook himself revealed how he had travelled in France and Spain, and stayed in the house of the theologian Diodati in Geneva. Only in the mid 1640s did he reappear, now in London, as an advocate of religious freedom and economic and legal reforms. He published a series of eloquent pamphlets in which he promoted these currently fashionable issues. He was unusual among law reformers for his familiarity with the work of the courts. Cook looked to the victorious parliamentarian army to accomplish change.
He attracted greater public notice, first in 1646 by acting for John Lilburne in his dispute with the house of lords, and then in January 1649 as solicitor for the state at the trial of Charles I. In print he proclaimed his republicanism. He was hostile not just to the person of Charles I, but also to the institution of monarchy. These views commended him to Oliver Cromwell (qv), who selected Cook for the chief justiceship of Munster early in 1650 after John Sadler had declined the post. Cook quickly took up office, earning praise for his achievements there. A system of decentralised county courts, the absence of paid barristers, payment of debts in instalments, and a blend of equity and common law were features that might usefully be copied by English courts. Little detail about the functioning of the Munster court survives. In the aftermath of war, Cook's scope for innovation was wide. If poorer litigants benefited, there are hints that the prosperous were penalised.
Cook, with his legal expertise, was drawn into other administrative tasks. His reforming ideals persisted and made him uneasy about the growing traditionalism of Irish government, especially after the arrival of Henry Cromwell (qv) in 1655. At this juncture, Cook was invited to serve in the newly restored Four Courts in Dublin, as second justice in the court of upper bench (successor to the king's bench). He refused, and in doing so he restated his commitment to cheaper and easier justice, such as the Munster presidency had dispensed. His long statement (6 August 1655) abounds in detail about prewar and recent legal procedure. It also constitutes the only extended application of English ideas of law reform to seventeenth-century Ireland. Despite declining the judgeship, in January 1656 Cook served as a commissioner in the court at Athlone for hearing claims to land. Later in the same year he was invited to become, and is mentioned as, recorder of Waterford. It is unlikely that he ever acted in that capacity. Between April 1657 and the spring of 1659 he was in England, probably settling his private affairs. He may also have gravitated to his old republican acquaintances, hostile alike to the Cromwellian protectorate and the conservative tenor of Henry Cromwell's Irish administration. Early in 1659 he was again considered as a candidate for the Irish judiciary. Appointed to the post he had declined in 1655, he found his load lightened by the suspension of most legal processes in the confusion of 1659. Prominent among the radicals who now ran Ireland on England's behalf, in December 1659 he was a target in the coup that toppled the Dublin executive. He was sent as a prisoner to England. There, after Charles II's restoration, his implication in and abiding support for the regicide marked him out. Tried on 13 October, he was executed in London on 16 October 1660. The Irish estates that he had received during the interregnum were automatically forfeited.
An engraved portrait by an unknown artist is in the National Portrait Gallery, London; another, together with a portrait medal by Thomas Simon, is in the British Museum.