 From 1895 to 1935, Llanarmon Dyffryn Ceiriog was in the Llansillin Rural District, which merged in 1935 with Chirk Rural District to form the Ceiriog Rural District.Llanarmon Dyffryn Ceiriog was in the Ceiriog Rural District from 1935 to 1974.In 1974, Denbighshire was abolished as an administrative county, and Llanarmon Dyffryn Ceiriog was incorporated into the Glyndŵr District of the new county of Clwyd.