Kingdom in western Wales;
- A district in the county of Dyfed, 1975-96;
- A unitary authority and county since 1996.
According to legend the Kingdom was ruled by the descendants of Ceredig, one of the sons of Cunedda, the King of 5th century Wales. It extended from the Tyfi (Dovey) to the Teifi. In the 8th century, Seisyll, a member of the dynasty, expanded into neighbouring Ystrad Twyi (Valley of the Towy) and the enlarged Kingdom was known as Seisyllwg after him. Later the southern Kingdom became known as Deheubarth and extended even further.
The Norman advance into western Wales led to the loss of the southwestern corner of the old Ceredigion Kingdom in the late 11th century, and so, except for the last thirty-five years of the 12th century, the town of Cardigan was lost to Welsh rule. For some years in the early 12th century much of Ceredigion fell to the Normans led by Gilbert de Clare but in the 1130s it came again under the control of Deheubarth.
In the 13th century it was the north Welsh Principality of Gwynedd that held Ceredigion. The destruction of Gwynedd as a state in 1282 led to an English Principality of Wales, in which Ceredigion and the royal lands around Cardigan together became the county of Cardiganshire.
When in 1975 Cardiganshire became a district in the new county of Dyfed, it changed its name back to Ceredigion, and in 1996 became a unitary authority, with the status of a county.