[4] The name persisted in the post-Roman Kingdom of Dyfed (clearly a continuation of this pre-Roman etymon) and even survived the Norman conquest of Wales and the introduction of the Shire system, with Thomas Morgan noting that the Welsh inhabitants of Pembrokeshire still referred to the area as Dyfed in the nineteenth century.

It was originally created as an administrative county council on 1 April 1974 under the terms of the Local Government Act 1972, and covered approximately the same geographic extent as the ancient Principality of Deheubarth, although excluding the Gower Peninsula and the area west of the River Tawe.

The administrative headquarters of Dyfed County Council was Carmarthen, whilst the largest settlement was Llanelli.

It is bounded by the preserved counties of Gwynedd to the north, Powys to the east and West Glamorgan to the southeast.

Ceredigion, the northernmost part of Dyfed, has a narrow coastal strip and the Cambrian Mountains cover much of the east of the county.

Further south in Ceredigion the land is less mountainous, and the River Teifi forms the border with Carmarthenshire for part of its length.

The south coast has many fishing villages and sandy beaches and the eastern part around Llanelli and Burry Port is more industrial.