Dyfed is a late 20th/21st century county of Wales.
The Local Government Act 1972 caused the county of Dyfed to be created on April 1, 1974. It covered the former administrative counties of Cardiganshire, Carmarthenshire, Pembrokeshire which were divided into local government districts as so :
Districts in 1974
Carmarthen, Dinefwr, Llanelli
Preseli, South Pembroke
The Lord Lieutenant of Dyfed had previously been the Lord Lieutenant of Pembrokeshire, with the Lord Lieutenant of Cardiganshire and Lord Lieutenant of Carmarthenshire becoming Lieutenants. The Dyfed-Powys Police had been created a number of years earlier.
The Local Government (Wales) Act 1994 broke up Dyfed into three unitary authorities on April 1, 1996 : Cardiganshire (which renamed itself Ceredigion as soon as it was able), Carmarthenshire and Pembrokeshire, but retained Dyfed as a preserved county for a few purposes (such as Lieutenancy).