Llanidloes takes its name from the early 7th century Celtic Saint Idloes (Llan-Idloes = the Parish of St Idloes), after whom its parish church is named. The village hall is the centre of Wales.It was then part of the cantref of Arwystli. In 1280 Llanidloes received a market charter from the King (granted to Owen de la Pole) and the benefit of Edwardian town planning and earthwork defences. The present-day street plan follows the 13th century grid layout. O’Neill traced earth bank defences from the confluence of the Severn with the Clywedog and along Brook Street on the north, beyond High Street on the east, and along Mount Street on the south; with the Severn forming the western boundary. He suggested that the medieval castle with its bailey lay immediately to the south in the area of Mount Street. However, the precise positioning of the Castle and earthen bank defences needs to be verified by archaeological evidence. The town prospered and was granted borough status at about this time, and by 1309 there were 66 burgesses. Revival after the Glyndwr uprising was slow, but there were 59 taxpayers in 1545.
The following centuries saw the growth of weaving and flannel production. This was essentially a cottage industry, and the local products were sent to market in Shrewsbury. Towards the end of the 18th century, Llanidloes was the largest producer in Montgomeryshire, but after about 1810, with the introduction of factories, which brought all the processes under one roof, Newton gradually overtook Llanidloes as the main centre. Some of the three-storey houses with brick façades of this period would have housed weaving lofts on the upper storey Lewis’s Topographical Dictionary of 1833 noted that there were forty carding engines, eighteen fulling mills and thirty-five thousand spindles .. affording considerable employment in Llanidloes. But the new technology was far from profitable, and the factory system led to increasing unrest, which culminated in the Chartist riots in 1839. Newtown, connected to the Montgomeryshire Canal in 1819, soon became the centre of the flannel industry in Wales with the opening of its Flannel Exchange in 1832. Llanidloes followed suit in 1838 when former Public Rooms in Great Oak Street were built by a local consortium as a Flannel Exchange; but this only lasted a few years, although Llanidloes flannel was regarded as of the better quality. Some owners, particularly Thomas Jones, who owned the Cambrian and Spring Mills, struggled to promote the Llanidloes flannel industry, but by 1913 the last mill had closed.
Lead mining became the more profitable industry from 1865, when rich deposits were discovered at the Van mines. By 1876, the mines were among the most productive in the world, employing over 500. Important too was the town’s iron foundry, established in 1851. This second phase of prosperity is well reflected in the townscape, most notably in the proliferation of fine chapels, built during the 1870s. Commercial success is reflected by the many fine shopfronts that survive from the later part of the 19th century. But again decline set in: printing and tanning gained in importance, but the last of the mines closed in 1921. Little has changed since then, except the building of houses, including a Garden Suburb and a new school. The building of the by-pass in 1991, along the track of the former railway, has largely protected the town from the ravages of traffic. Llanidloes has attractive tree-lined main streets, originally planted in 1901, although many of the trees have been replaced. The vibrant community, pleasantly varied streetscape and attractive setting makes Llanidloes one of the nicest towns in Wales.