THIRSK, a market-town in the Thirsk and Malton parliamentary division of the North Riding of Yorkshire, England, 22 m. N.W. by N. from York by the North-Eastern railway. Pop. (1901) 3093. It lies in a fertile plain W. of the Hambleton Hills, on the Codbeck, a small tributary of the Swale. The church of St Mary, entirely Perpendicular, with parvise, chancel, nave, aisles, porch, and tower 80 ft. in height, is one of the most beautiful churches in the Riding. The original work of oak is especially noteworthy. The moat of the ancient castle built by the Mowbrays about 980 remains. The principal modern buildings are the assembly rooms, mechanics' institute, and court-house. Standing in the fertile district of the Vale of Mowbray, the town has an extensive agricultural trade. Agricultural implements are largely manufactured. Iron-founding, engineering, tanning and brick-making are carried on, and there are large flour-mills.

At the time of the Domesday Survey, Thirsk (Treske) was a manor of little importance belonging partly to the king and partly to Hugh, son of Baldric. Soon afterwards it was granted to Robert de Mowbray, who often resided there, and is said to have raised the castle round which the borough grew up. His estates, being forfeited for treason against William Rufus, were restored by Henry I. to Nigel de Albini, Robert's cousin, who took the name of Mowbray. Roger, son of Nigel, took part in the rebellion against Henry II. in 1174, and although he was allowed to retain his estates, his castle at Thirsk was destroyed. The manor remained in his family until the death of John de Mowbray, duke of Norfolk, without issue male in 1475, and after passing through several families was finally sold in 1723 to Ralph Bell, whose descendants thereafter held the manor. Thirsk is first mentioned as a borough in a charter granted by Roger de Mowbray to Newburgh Priory in the reign of Henry II. It was governed by a bailiff elected by the burgesses at the court leet of the lord of the manor, and never received a charter of incorporation. The burgesses were represented in parliament by two members in 1295 and again from 1552–53 to 1832, when by the Municipal Reform Act the number was reduced to one. In 1885 the town was disfranchised. Roger de Mowbray held a market by prescription in Thirsk in the 13th century, and by Camden's time (c. 1586) it had become one of the best markets in the North Riding. It is still held by the lord of the manor.

See Victoria County History: Yorkshire; William Grainge, The Vale of Mowbray: a historical and topographical account of Thirsk and its neighbourhood (1859).