Clun takes its name from the river running through it, the name itself coming from the very early Brythonic root that also produced the Lancashire and Essex rivers called Colne. The Anglo-Saxons built a church here around the end of the 7th century on what is now the south bank of the river, on the high ground around St George's Church. Scattered settlement in the surrounding hills goes back to the Neolithic, more than five thousand years. For centuries Clun sat on the great drove road by which Welsh flocks were driven east to the markets of the English Midlands and London. The town's two halves, Saxon south of the river and Norman north of it, were connected in the 14th century by a stone packhorse bridge so well built that it still carries the A488 today, almost every stone original.

When the Normans took the land after the Conquest, Edric the Wild's confiscated estate was given to Roger de Montgomery, who passed Clun on to Picot de Say. The de Says raised the castle whose ruin still dominates the bend of the river to the north, and Clun became the seat of a Marcher Lordship governed by its own law rather than the king's. The lord of Clun could execute criminals on his own authority, a privilege so unusual that condemned men were brought from as far as Shrewsbury to be hanged here. The lordship eventually passed to the Fitzalans, then to the Howards, and the Duke of Norfolk holds the title Baron Clun to this day. Through the medieval centuries the town shrank and grew with the fortunes of the castle. By the Tudor period the castle was a ruin and the town was settling into the agricultural quiet that defines it now.

Sir Walter Scott is said to have stayed at the Buffalo Inn here while writing parts of The Betrothed in the 1820s, basing his fictional fortress Garde Doloreuse on the ruin above the town. The Buffalo has been shuttered since 2004 and waits empty for someone to know what to do with it. E.M. Forster visited and turned Clun into Oniton in his 1910 novel Howards End. Malcolm Saville set his Lone Pine Club children's adventure books in and around Clun. Bruce Bairnsfather, the cartoonist who created the muddy, mustached Old Bill character that defined the British soldier's view of the First World War, lived at Cresswell House through the Second. John Osborne, the playwright who detonated the British stage with Look Back in Anger in 1956, lived just down the valley in Clunton and died there in 1994. Quietness has its uses for people who write.

Modern Clun keeps itself busy in small ways. Over the May bank holiday the Green Man festival sees a man in foliage cross the bridge to do ritual battle with the spirit of winter, and a May Fair fills the castle grounds with a May Queen and stalls. The last weekend in June, around twenty private gardens open for Clun Open Gardens with cream teas and plant sales. In August comes the Clun Carnival, with marrow and Victoria sponge competitions in the show tent and a procession through the streets. The first weekend in October brings the Clun Valley Beer Festival, six pubs from Anchor to Aston on Clun pouring local ale. There are two cafes, one on the bridge, a primary school, a museum in the old Town Hall, the 17th-century Trinity Hospital almshouses on Hospital Lane, and Clun Mill, the so-called malevolent mill of local legend, now a youth hostel. The malevolence is in the name only. Mostly what Clun has is itself: a small town on a quiet river, half-Saxon and half-Norman, the castle in ruins above it and Housman's verse still hanging over the hills.