Carmarthenshire (Welsh: Sir Gaerfyrddin or Sir Gâr) is a unitary authority in the south west of Wales and the largest of the thirteen historic counties. The three largest towns are Llanelli, Carmarthen and Ammanford. The county town and administrative centre of Carmarthenshire is Carmarthen and the most populous settlement is the area in and around the town of Llanelli. With its fertile land and agricultural produce, Carmarthenshire is known as the "Garden of Wales".
Carmarthenshire has its early roots in the region formerly known as Ystrad Tywi (Vale of [the river] Tywi) and part of the Principality of Deheubarth during the High Middle Ages, with the court at Dinefwr. Following the Edwardian Conquest of Wales, the region was reorganized by the Statute of Rhuddlan in 1284 into Carmarthenshire.