The parish of Cefn includes the villages of Cefn Mawr, Cefn Bychan, Acrefair, Penybryn, Newbridge, Plas Madoc and Rhosymedre and is situated on the northern slopes of the Dee Valley. As well as the former industrial villages around Acrefair, it also includes some rural areas to the north on the slopes of Ruabon Moors. At the time of the 2001 census, it had a total population of 6,669 in 2,763 households.
The area formerly comprised the townships of Coed Cristionydd and Cristionydd Cynrig (or Cristionydd Kenrick), which became part of the parish of Ruabon. Parts of the townships were formed into the new parish of Rhosymedre in 1844.