Originally built in the late-seventeenth century as a mansion house for the Humphreys family, Bodelwyddan Castle was purchased in c.1690 by Sir William Williams (1634?1700). The mansion remained largely unaltered throughout the eighteenth century ? an image of the building from the 1781 eight-volume illustrated edition of Thomas Pennant's Tour in Wales shows a double-pile house consisting of two storeys and attic with dormered attic windows and prominent chimneys. There were two advanced wings at the ends of the south-east front, flanking the facade containing a central entrance.

The south-east front was altered in 1805 by Sir John Williams (First Baronet) who remodelled the house in the Greek Revival style and added a Doric loggia to the central bays of the south-east facade. Further and more drastic alterations occurred under his son, Sir John Hay Williams (1794?1859). Under the architectural direction of Hansom and Welsh from the early 1830s to the early 1840s, the structure was enlarged and transformed into a nineteenth-century Gothic castle with stone facing, castellated parapets and turrets and curtain walls as well as statuary, although elements of the earlier nineteenth-century remodelling survive both inside and out. (For wings within the curtain walls see NPRNs 54203-54220 and 54232.) In c.1860, the castle became the seat of a model estate under Lady Margaret Willoughby de Boke (daughter of Sir John Williams of Bodelwyddan Castle). Although the family's finances had become stretched by the late nineteenth century, in part owing to the decline of their lead mining interests, the house was further remodelled in 1876 by Sir William Grenville Williams. The estate was sold in 1918 by Sir William Willoughby Williams.

The grounds were utilised by the Army during the First World War, and the practice trenches constructed there were reconstructed in the grounds in 2015. After the war, the property passed to the War Office before being leased in 1920 by Florence Lindley and becoming Lowther College, a private school for girls which purchased the freehold to the property in 1925. The school closed in 1982 and the freehold was purchased later in the 1980s by Clwyd County Council. Part of the main house and outbuildings became the Bodelwyddan Castle Hotel with new structures built to the south and west of the main house. The remainder of the house, under the direction of the Bodelwyddan Castle Trust, houses a museum and art gallery.

An 1871 map shows a private gasworks in the NW corner of the Castle site. An article from the 14th of January 1905 in the Denbighshire free press, mentioned the gas lighting in Ball room. The gasworks were featured on the maps until the 1954 OS map. These private gasworks supplied gas to light the castle and estate. They are likely to have been installed during the ownership of the Castle by Sir William Grenville Williams.  

(Sources: Cadw Listed Buildings Database, 1383; Dictionary of Welsh Biography Online, s.v. Williams, Sir William (1634?1700); Thomas Pennant, Tour in Wales, 8 vols. (1778?1781) (Digitized by the National Library of Wales); Edward Hubbard, Buildings of Wales: Clwyd (Cardiff: University of Wales Press, 1986), p. 325)
A.N. Coward, RCAHMW, 02.01.2019