St Clears is a small town on the River Tâf in Carmarthenshire, Wales. According to the 2001 UK census, it has a population of 2,820 people, most of whom are Welsh-speaking, although there is a marked difference between the southern and northern ends of the town in percentage terms.
The Norman St Clears Castle was constructed in the twelfth century (the castle mound can still be seen) and the town, which was a Marcher Borough, grew around it. Below the castle there was a port on the river Tâf, which could take ships of up to 500 tons according to a plaque at the site. The castle held out against Owain Glyndŵr.
Nearby Trefenty house became the home of a branch of the Perrot family in the 16th century, and it was here that the amateur astronomer Sir William Lower and a neighbour, John Protheroe, set up one of Britain's first telescopes in 1609, which they used to study the craters of the Moon and Halley's Comet.
In 1842, one of the local toll gates was destroyed in the Rebecca Riots.
The building of the railway was responsible for the decline of many of the small ports along the Bristol Channel coast, and St Clears was no exception. The railway passed about 2 miles north of the castle, and new building at the north end of the high street spread eastwards along Pentre Road, and then northwards again to the station. Pentre Road is now the main commercial centre of the town, and was formerly part of the A40 road until construction of the dual carriageway bypass.
The town's Cattle market was important until its closure, but the town still has a large agricultural cooperative store. The town has also hosted an oil distribution centre and milk processing plant. Now smaller industrial units provide the main local employment.