CLONSILLAGH, a parish, in the barony of CASTLE-KNOCK, county of DUBLIN, and province of LEINSTER, 7 miles (N. W.) from Dublin ; containing 954 inhabitants, and comprising 2943 statute acres, the whole of which is arable land. There are limestone quarries in the parish, and an extensive flour-mill on the Liffey, erected on the site of a very ancient one, called "the Devil's Mill," from its having been erected, according to tradition, in one night. The Royal Canal passes through the parish. Woodlands, formerly called Luttrell's Town, and the seat of the Earls of Carhampton, is now the property and residence of Col. T. White. The demesne includes above 648 statute acres, exceedingly picturesque ; the mansion is a noble building, in the castellated style, and is said to contain a room in which king John slept : that monarch granted the estate to the Luttrell family. In a glen, a stream, which is supplied from a beautiful lake in the park, of 20 acres, rolls over a rocky bed and forms a cascade about 30 feet high. The other seats are Coolmine, the residence of A. Fitzpatrick, Esq. ; Clonsillagh, of R. H. French, Esq. ; Broomfield, of the Rev. S. Thompson ; Clonsillagh, of Ignatius Callaghan, Esq. ; Hansfield, of T. Willan, Esq. ; and Phibblestown, of Capt. H. Reid, R. N. The parish formerly belonged to the priory of Malvern, in Worcestershire. It is a rectory, in the diocese of Dublin, and is part of the union of Castleknock : the tithes amount to £240. The church is a small neat building. In the R. C. divisions it also forms part of the union or district of Castleknock, and has a neat chapel at Porterstown, built by the late L. White, Esq., who also built a school-house, with apartments for the master and mistress : the school is supported by subscription, and there is one on the lower road, near the Liffey ; they afford instruction to about 90 children.