"A parish in the Union and hundred of Ruthin, county of Denbigh. ..... It is situated in the southern portion of the county, and is intersected by several small streams, which, rising in the circumjacent hills, unite within the parish, and, flowing in a north-easterly direction, fall into the river Clwyd. It comprises a moderate extent of arable and pasture land in a good state of cultivation." [A Topographical Dictionary of Wales, 1833 & 1849, Samuel Lewis]
Cyffylliog was a chapel of ease to Llanynys until 26 January 1874, when it was established as a separate parish, comprising the townships of Bontuchel, Trefor (or Cefntrefor), Treganol (or Fachlwyd), Ffiddoedd and Tre'r Parc; which until then had been in the parish of Llanynys.
To all intents and purposes, Cyffylliog had already functioned as a separate parish for many years.
In 1878, a further 2007 acres were added to Cyffylliog from the parish of Llanrhaeadr yng Nghinmeirch.