The modern Gwynedd was originally created on April 1, 1974 under the Local Government Act 1972. It covered the entirety of the former administrative counties of Anglesey, and Caernarvonshire along with all of Merionethshire apart from Edeyrnion Rural District (which went to Clwyd), and also a few parishes in Denbighshire: Llanrwst, Llanstaffraid Glan Conway, Eglwysbach, Llanddoget, Llanrwst Rural and Tir Ifan.
In the latest round of local government reorganisation, on April 1, 1996, it was reconstituted to cover a different area, losing Anglesey to became an independent unitary, and Aberconwy to the new Conwy county borough.
As the new Gwynedd covers most of the traditional counties of Caernarfonshire (less the part in the borough of Conwy) and Merionethshire, the reconstituted area was originally named Caernarfonshire and Merionethshire. As one of its first actions, the Council renamed it Gwynedd on April 2.