St. Brigid is the patron saint of the village.
Mythic Milesian period
"During the Milesian era Castleknock is named as one of twenty-five places at which Conmhaol of the race of Eber, while holding the sovereignty of Ireland, defeated in battle the descendants of Eremon,' and a Celtic writer mentions that Castleknock was sometimes known as duma meic Eremon, or the duma of the sons of Eremon.' The mention of a duma shows that there was at a very early time an eminence of note at Castleknock ; the duma may have been, Mr. Westropp observes, used for purposes of residence, sepulchre, or outlook, or, as in the case of Duma Selga, for all three."
In a poem relating to the earliest centuries after Christ the origin of the name Cnucha is connected with Conn of the Hundred Battles, and the name is said to have been borne by his foster-mother: —
The Barony of Castleknock was originally a feudal lordship created in the 12th century for the Tyrell family; it passed by inheritance to the Burnell family. The first Baron, Hugh Tyrrel, gave lands in the barony at Kilmainham to the Knights of St. John who continue in the area today in the form of St. John Ambulance. Later, civil parishes, based on the boundaries of the Ecclesiastical parishes of the Established church were used to sub-divide the barony. This table lists the nine civil parishes of the barony.
Note 1: the entire barony lies north of the River Liffey. The parish of St Jude's, which consists of six townlands, is situated on both banks of the Liffey. The only part of the parish that lies to the north of the Liffey is a field of 499 acres in the south-eastern corner of the Phoenix Park as well as a thin strip of 49 acres between the Chapelizod road and the river - the townland of Longmeadows. According to the 6 inch historical maps from the Ordnance Survey of Ireland that were created in 1829, no such parish exists. Only the later map of 1889, at a scale of 25 inches, displays the parish.
Within the civil parish of Castleknock, there are 22 townlands per the table below.
Castleknock was a rural village in western County Dublin until the late 1960s, when the first housing estates began to be developed. Castleknock developed in tandem with neighbouring settlement Blanchardstown, both of which grew rapidly from the early 1970s to the present. During the 1970s and 1980s, the village became subsumed into the suburban fabric of Dublin.
Local representatives have criticised developments which they say are to the detriment of the local character and integrity of the village.
In February 2010, there were concerns about the fate of the old post office when hoarding was erected around the site. However, "proposed work involves a high quality restoration of the building to its former state after many years during which it has remained vacant."