Letters exchanged between members of the Maurice and Owen families of Clenennau and Brogyntyn, and other correspondence from friends or associates in Wales and England, together with a number of important official documents deriving from county administration in Caernarfonshire during the Tudor and Stuart periods, 1485, 1573-1698. Many of the early letters and papers, 1580-1622, relate to the joint deputy lieutenancy in Caernarfonshire of Sir William Maurice and Sir John Wynn, showing their preoccupation with the raising and organisation of militia troops for the defence of Caernarfonshire and for despatch to Ireland. Other topics include Sir William Maurice's position as deputy vice-admiral of North Wales and the protracted civil lawsuits in which he was engaged. The collection also constitutes an important historical source for the conduct of the Civil War in North Wales. Items from that period primarily concern Sir John Owen and his brother, Col. William Owen, Royalist commanders at Conwy and Harlech respectively, and their subsequent treatment under the Commonwealth and Restoration, 1643-1666. Many of the letters from 1678 to 1698 reveal the life of Sir Robert Owen, his debts, estate business, cultural interests and attachment to the Jacobite cause, together with contemporary political news. Apart from individuals already mentioned, prominent correspondents include the Privy Council of Elizabeth I, mostly through Henry Herbert, President of the Council in the Marches of Wales, 1587-1600; Sir Henry Johnes of Abermarlais, 1605-1616; Ralph, Lord Eure, 1607-1617; members of the Brynker family, 1603-1681; the Wynn family of Glyn and Sylfaen, 1625-1697; the Anwyl family of Park, 1636-1693; Charles I, Prince Rupert and Prince Maurice, 1642-1647; Lord Byron, 1644-1648; John Williams, Archbishop of York, 1645-1646; George Twisleton, 1649-1660; the Godolphin family of Abertanat, 1658-1698; John Gadbury, 1679-1688; and Edward Lhuyd, 1696-1697.

Official letters and other papers mainly relating to Caernarvonshire, 1660-1661, comprising communications received from the Privy Council by Richard, 2nd earl of Carbery, Lord Lieutenant of Wales and Lord President of the Council in the Marches of Wales, and transmitted by him to the deputy lieutenants, etc., of Caernarvonshire, with reports of the meetings of the latter, letters sent by them to the high constables, and communications sent by them to each other. Among the correspondents are Sir Richard Wynne of Gwydir and Henry Maurice. Many of the documents relate to the militia in Caernarvonshire and include records of men subject to be called to the militia, lists of horses, arms, and ammunition available in the county, etc.

Official documents and other papers, 1675-1727, many of them addressed to the deputy lieutenants, etc. of Caernarvonshire and relating to the militia, musters, the confiscating of weapons in the possession of Papists, etc. Among the correspondents are Henry, 3rd marquis of Worcester and first duke of Beaufort, Lord President of the Council in the Marches of Wales, Col. Thomas Mostyn of Gloddaeth, John Wynne of Whitehall, mustermaster for Caernarvonshire, and Richard, 3rd baron Bulkeley of Baron Hill. The documents include a statement by Thomas Glynne relating to a 'conventicle' at the house of Ellis Owen, Llangybi, at which James Owen preached; a memoranandum by Thomas Mostyn relating to the refusal of William Wynne, sheriff of Flintshire, to read the proclamation of King George II at Holywell; and some papers of general North Wales interest.

Letters to Sir William Maurice and a number of drafts or copies of outgoing correspondence, 1587-1619, and a single letter to Lady Elen Eure, 1624. Items of interest include a water bailiff 's report on shipwreck timber found along the shores of Anglesey and Caernarfon; an application by the burgesses of Harlech to obtain an act of parliament for holding the Merionethshire [Great] Sessions and Quarter Sessions there, and to get royal confirmation of the town charter and fee farm, 1604, with letters from Griffith Vaughan on the technical difficulties of implementing the same, 1611; Sir Henry Lee on a dispute over lands held by William Maurice from the Corporation of Harlech, 1591; William Thomas on the subsidy roll accounts, with a summary of deputy lieutenants in other counties of Wales and England, 1602; John Wynn of Gwydir and others, with copies of William Maurice 's outgoing letters to county and government officials, emphasising the difficulties encountered by the deputy lieutenants in mustering troops and collecting mises in Caernarfonshire against a possible Spanish invasion, and for the suppression of rebellions in Ireland, 1587-1602; and a draft request to Anne, Countess of Warwick, to use her influence in obtaining a position for William Maurice 's son [pre-1588].

A group of submissions from the War Office to Queen Victoria relating to the Royal Anglesey Militia, 1867; the Denbighshire Regiment of Yeomanry Cavalry, 1876; the militia regiments of Denbighshire and Merioneth, 1876; the militia regiments of Radnorshire and Brecknockshire, 1876; the Royal Carnarvon Regiment of Militia, 1876; the Royal Cardigan (Rifle) Militia, 1877; the Royal Anglesey (Light Infantry) Militia and the Royal Anglesey Engineers Militia, 1877; etc. All the submissions carry notes of approval in the hand of theQueen. Also included in the group are a schedule of establishments of Welsh militia regiments [c. 1867], and an explanatory memorandum, 1867, by J[onathan] Peel, secretary at war, touching the wish of the lords lieutenant of the Welsh counties to return to the old system of independent corps.

Personal papers and especially papers relating to the public offices of members of the Wynn family of Gwydir, Caernarfonshire. These include letters and orders from the Privy Council and from Thomas Gerard, Ralph Eure, William, earl of Northampton, etc., as Lords President of the Council of Wales and the Marches to Sir John Wynn, 1st baronet, relating to the government of Caernarfonshire and the mustering of soldiers for various wars. The papers from the reigns of Henry VIII, Edward VI and Mary chiefly relate to preparations for wars in Scotland and France, whilst the papers from the reign of Elizabeth I chiefly relate to preparations for wars in Ireland and against Spain. The archive also includes papers relating to the Civil war and to elections in Caernarfonshire. The archive is an important source for local administration in late sixteeenth and seventeenth century Wales and for the relationship between local and central government. Most of the papers relating to the Gwydir estate for this period have not survived.