Though of ancient origin, Blois is first distinctly mentioned by Gregory of Tours in the 6th century, and the city gained some notability in the 9th century, when it became the seat of a powerful countship with «Blesum castrum» («Le château de Blois»). In 1171, Blois was the site of a blood libel against its Jewish community that led to 31 Jews (by some accounts 40) being burned to death. Their martyrdom also contributed to a prominent and durable school of poetry inspired by Christian persecution. In 1196, Count Louis granted privileges to the townsmen; a commune, which survived throughout the Middle Ages, probably dated from this time. The counts of the Châtillon line resided at Blois more often than their predecessors, and the oldest parts of the château (from the thirteenth century) were built by them. In 1429, Joan of Arc made Blois her base of operations for the relief of Orléans. Joan of Arc rode the thirty-five miles on Wednesday 29 April to Blois to relieve Orléans. After his captivity in England, Charles of Orléans in 1440 took up his residence in the château, where in 1462 his son, afterwards Louis XII, was born. In the 16th century Blois was often the resort of the French court. The Treaty of Blois, which temporarily halted the Italian Wars, was signed there in 1504–1505.
Blois was occupied during World War II by the German army, which took the city on 18 June 1940. The city was liberated by American soldiers during the last two weeks of August 1944. On both occasions, the city withstood several days of bombing.
The Château de Blois, a Renaissancechâteau once occupied by King Louis XII, is located in the centre of the city, and an 18th-century stone bridge spans the Loire. As Blois is built on a pair of steep hills, winding and steep pathways run through the city, culminating in long staircases at various points. To the south of the city, the Forêt de Russy is a reminder of the thick woods that once covered the area.