Dyfed was a historic administrative county of south-west Wales, created in 1974 by merging the ancient counties of Carmarthenshire, Cardiganshire and Pembrokeshire into a single large authority, and named after Dyfed, one of the most powerful and long-lived kingdoms of early medieval Wales, whose territory broadly corresponded to this same corner of the country. Carmarthen served as the county town of this modern administrative union, which lasted until 1996, when it was divided back into three separate unitary authorities largely, though not perfectly, restoring the boundaries of its constituent historic counties.
During its two decades of existence, Dyfed encompassed an unusually wide range of Welsh landscape and culture, from the industrial and coal-mining heritage of eastern Carmarthenshire, through the rich dairy farmland of the Tywi valley, to the rugged, Welsh-speaking coastline of Cardiganshire around Aberystwyth and Cardigan Bay, and the dramatically different character of Pembrokeshire's coast, much of it protected as Wales's only coastal National Park and containing a historic zone of English and Flemish settlement long nicknamed 'Little England beyond Wales'. This combination made Dyfed, even as an administrative creation, a genuinely coherent expression of south-west Wales's shared coastal and rural character.
St David's Cathedral, seat of the patron saint of Wales, and the university town of Aberystwyth, home to the National Library of Wales, gave Dyfed's territory a claim to be both the spiritual and, in a sense, the intellectual heart of Wales during the period the county existed. Although the name Dyfed ceased to denote a local authority after 1996, it continues in use for the region's police force and other public services, preserving a revived medieval kingdom's name in everyday currency across south-west Wales.