Ruthin ( ; ) is the county town of Denbighshire in north Wales. Located around a hill in the southern part of the Vale of Clwyd - the older part of the town, the castle and Saint Peter's Square are located on top of the hill, while many newer parts of the town are on the floodplain of the River Clwyd (which became apparent on several occasions in the late 1990s—new flood control works costing £3 million were inaugurated in autumn 2003). Ruthin also has villages on the outskirts of the town such as Pwllglas and Rhewl.
The name 'Ruthin' comes from the Welsh words rhudd (red) and din (fort), and refers to the colour of the new red sandstone which forms the geologic basis of the area, and from which the castle was constructed in 1277-1284. The original name of Rhuthin was 'Castell Coch yng Ngwern-fôr' (red castle in the sea-swamps).
There is evidence of Celtic and later Roman settlements in the area. However, little is known of the history of the town before construction of Ruthin Castle started in 1277 by Dafydd, the brother of prince Llywelyn ap Gruffydd, but he forfeited the castle when he rebelled against King Edward I with his brother; Edward's queen, Eleanor, was in residence in 1281. The Marcher Lord, Reginald de Grey, Justiciar of Chester, was given the Cantref (an administrative district) of Deffrencloyt (= Dyffryn Clwyd, the Welsh for Vale of Clwyd), and his family ran the area for the next 226 years. The third Baron de Grey's land dispute with Owain Glyndŵr triggered Glyndŵr's rebellion against King Henry IV which began on 16 September 1400, when Glyndŵr burned Ruthin to the ground, reputedly leaving only the castle and a few other buildings standing.
The Lord de Grey established a Collegiate Church in 1310. Now, the Collegiate and Parish Church of St Peter, it dominates the Ruthin skyline. The double naved church boasts two medieval carved roofs. The church is known for its musical tradition, it has a large choir of children and adults and a four manual Wadsworth-Willis Organ. Behind the church can be seen the old college buildings, school and Christ's hospital.
The half-timbered Old Court House (built in 1401), now a branch of the NatWest Bank, features the remains of a gibbet last used to execute a Franciscan priest, Charles Meehan, also known as Mahoney. He was shipwrecked on the Welsh coast when Catholicism was equated with treason — Meehan was hanged, drawn, and quartered in 1679. He was beatified by Pope John Paul II in 1987 as one of the Eighty-five martyrs of England and Wales.
During the English Civil War the castle survived an eleven-week siege, after which it was demolished by order of Parliament. The castle was rebuilt in the 19th century as a country house, and is now a luxury hotel, the Ruthin Castle Hotel.
From 1826 until 1921 the castle was the home of the Cornwallis-West family, members of Victorian and Edwardian high society.
In its 18th century heyday as a town on drovers' routes from Wales into England, Ruthin was reputed to have "a pub for every week of the year". By 2007, however, there are only eleven pubs in the town.
In 1863 the Denbigh, Ruthin and Corwen Railway, which linked in Denbigh with the Vale of Clwyd Railway (subsequently part of the London and North Western Railway, the London, Midland and Scottish Railway, and British Rail) reached the town. The route ran from Rhyl on the north coast, through Denbigh and Ruthin to Corwen. Thereafter the line joined a route from Ruabon through Llangollen, Corwen and Bala to Barmouth. The railway and Ruthin railway station closed in 1963 as part of the Beeching Axe. The site of the town's railway station is now occupied by a large road roundabout (Brieg Roundabout) and the Ruthin Craft Centre which originally opened in 1982 but was rebuilt and reopened in 2008 .
Sir Henry Haydn Jones MP (1863–1950) politician, slate quarry owner, and owner of the Talyllyn Railway was brought up in the town. He is immortalised for children as Sir Handel, owner of the Skarloey Railway in Rev. W. Awdry's Railway Series.