Under the Local Government Act 1972, the historic county of Merionethshire was abolished, for both local government and ceremonial purposes, on April 1, 1974. Most of the former county became part of the newly-formed county of Gwynedd, but the Edeirnion district, in the east, became part of the newly-formed county of Clwyd.

Following further local government reorganisation on April 1, 1974, most of the historic county of Merionethshire remained within Gwynedd, with the exception of the Edeirnion district which became part of the newly-created county of Denbighshire.