Ystradgynlais (Welsh: [ˌəstradˈɡənlais], English: //) is a town in the south-west of the county of Powys, Wales. It is the second largest town in Powys, the largest being Newtown. It is situated on the banks of the River Tawe in the historic county of Brecknockshire.
Penybont Inn, Ystradgynlais
|Population||8,092 (2011 census)|
|Sovereign state||United Kingdom|
|Fire||Mid and West Wales|
The town was first recorded in 1372. The place-name "Ystradgynlais", meaning "vale of the river Cynlais" – may derive from cyn (a chisel) and glais (a stream). Cynlais may also be a personal name.
Ystradgynlais is one of the few areas within the historic county Brecknockshire that has a reasonably high proportion of speakers of the Welsh language. According to the 2001 census, more than half of all the Welsh-speakers within the Brecknock district live in Ystradgynlais.