A piece of iron stamped 1612 was found in an old cinder bed on the Ynyscedwyn ironworks site suggesting that iron was smelted in the town during the reign of Elizabeth 1. The ironworks also provided cannon balls for use in the Napoleonic War. In 1837 George Crane and David Thomas developed the industry to use local anthracite coal in the production of iron. David Thomas, superintendent of the works under George Crane, emigrated to Pennsylvania and established the Leigh Crane Iron Company using the method developed at Ynyscedwyn. The town thus rightly claims to have played a significant part in the development of the vast iron and steel industry of America. The buildings on site have now been demolished leaving two rows of arches - the remains of a proposed steel making plant. The landscaped site is now a recreation area and the community hospital, opened in 1986, now occupies part of the site. This hospital replaced Craigynos Hospital some five miles north of the town, which was the former home of Adelina Patti, the world famous opera star of the 1880s. The Hospital is centre for a number of health clinics and has a minor injuries unit.
The ironworks site was owned by the Gough family of Ynyscedwyn House located approximately half a mile away.
In 1886 Richard Dancey Aubrey Fleming Gough married Cecil Clare Jones. He served as a Lieutenant Colonel in the 1st Territorial Battalion of the South Wales Borderers from 1887 to 1910. He died in 1933, at the age of 88, with no children. The Estate and House then passed out of theGough ownership. The house was then acquired by the Anglo-Celtic Watch Co. and was used as a guest house for business visitors. This came to an end in 1969 when it was converted to Council Offices by the Ystradgynlais Rural District Council which then became Brecknock Borough Counci. The Council’s Ystradgynlais offices were then transferred to a base at Trawsfordd until in 1974 when Powys County Council was established. Powys C.C. sold the former mansion in the 1990’s and was demolished in 1997.
A stone’s throw away from the Ynyscedwyn House was Maesydderwen a mansion, built by Patrick Moir Crane, the adopted son of George Crane, in 1847. The site was
eventually purchased by the former Breconshire County Council in 1909 to establish in 1911 the Ystradgynlais County School. The mansion was severely damaged by fire in February 1932 but was soon rebuilt to house the pupils. This building was then incorporated into a new building in 1954 to form Maesydderwen Comprehensive School. By 2013 Ysgol Maesydderwen, the community’s only secondary school,has been totally renovated. The site is also the location of the Ystradgynlais swimming pool and Sports Centre.
Following the Second World War a large factory was erected on the Ynyscedwyn Estate for the manufacture of watches and clocks. The factory, known locally as the ‘tick-tock’, exported the watches and clocks were world wide. The factory was probably the largest employer in the area with almost 2,000 persons employed at the site. This factory closed in 1980 but the site was occupied by subsidiary companies until 2010 when it was demolished and a supermarket constructed on the site.
The Woodlands Business Park has been constructed on part of the Ynyscedwyn Estate to the rear of the former ‘Tick –Tock’ factory and provides a pleasant working environment for a number of manufacturing businesses.
Arguably the town developed as a result of the heavy industries of coal and iron. These sites have now been cleared and the landscaped area redeveloped to parkland as at the Diamond Park, the site of the Diamond and Gurnos coal mines. Adjacent to the Diamond Park is the Wern Plymis Nature Reserve maintained by the Brecknock Wildlife Trust
The Gorsedd Park is located near the town centre and was opened after hosting the National Eisteddfod of Wales in 1954. In the park is the District War Memorial commemorating the names of those who lost their lives in the Service of their Country in the two World Wars. The park is also the location of the Cofio’r Glowyr –Remembering the Miners Memorial which outlines the history of the mining industry of the Upper Tawe and Twrch Valleys.
Glanrhyd was the site of the first Roman Catholic Church in the area built in 1911. The church, constructed of corrugated steel sheets, has since been demolished and a house built on its site. The new R.C. Church, built in 1939, is located nearer the centre of Ystradgynlais. A stone’s throw from this site is Ysgol Bro Tawe, opened in September 2012, on the site of the former Glanrhyd Primary School which opened in 1951. Prior to this pupils of primary school age were educated in nearby Libanus chapel. The former Glanrhyd school was demolished in August 2012.