The village is named from the eponymous 6th-century Saint Cynon and the Parish Church, which is basically pre-Reformation but heavily "restored" in the 19th century, and is built on an oval shaped hillock of pre-historic significance, is named in his honour; there is also a Calvinistic Methodist (Presbyterian) Chapel called Bethany. The nearby country house is Gregynog Hall, which dates from 1840; in the 19th century it was the seat of the Blayney Hanbury-Tracy families and became the centre of Welsh cultural life in the 20th century under Miss Margaret and Miss Gwendoline Davies, who had inherited the fortune of their grandfather the industrialist David Davies of Llandinam. Although it is commonly thought that they made the village alcohol-free and made the local pub into the Temperance Hotel, it is a fact that the Temperance Hotel existed from at least the 1880s. They used their money and influence to promote their faith by regular Chapel attendance and encouraging this among their tenants and employees and paying for the erection of the Manse near to the Bethany Chapel and installing its organ. They gave refuge to wounded soldiers in both World Wars and established a printing press and local choir. They left their home to the university of Wales and a cultural, educational and retreat centre.
Tregynon boasted a number of prolific local families in the agricultural and local industrial 19th and 20th centuries, including the Williams, Stephens, Thomas and Corfield "clans". The Brook, known as the Bechan in Welsh, is an eventual tributary of the Severn and provided power for the local Sawmill, now owned by Coed Cymru.
The latter decades of the twentieth century saw an expansion of the population of the village with many houses and bungalows being built in the low-lying fields. The presence of the local primary school, Ysgol Rhiw Bechan, for the area as well as the Village Community Hall are attractions to outsiders to settle. The centre of the village retains its old charm with the Rectory, Church House, old School displaying traditional half-timber framed black and white dwellings and innovative early use of concrete - the latter also found on the outskirts of the village in a pair of cottages. One of the oldest buildings is the Old School House, also known as "Tithe Barn", now divided into two homes, located alongside the remains of a mediæval fort with earthworks near the Bechan brook. Some of the straighter local roads are likely to be of Roman origin - leading to Llanfair Caereinion in particular.
Further from the centre of the village are a number of Farms including Ty'n y Bryn, Neuadd Llwyd, Cefn Llydan, etc.