The county got its name from Simon de Montfort, 5th Earl of Leicester, who played crutial role in England between 1160 and 1218.
He was the son of Simon de Montfort, lord of Montfort l’Amaury in France near Paris, and Amicia de Beaumont, daughter of Robert de Beaumont, 3rd Earl of Leicester – the de Montfort line itself descends from the Counts of Flanders.
He was present at the siege and subsequent massacre at Béziers on 22 July 1209 when the entire population of twenty thousand Cathars and Catholics were slaughtered. Thousands sought sanctuary in the Cathedral of St Nazaire which was set on fire and also in the Eglise de la Madeleine inside which all were butchered to death.”Tuez les tous, Dieu reconnaitra les siens” – “Kill them all, God will recognize his own” was the famous quotation which exonerated the rampaging Crusaders. Ironically it was Ste Madeleine’s Day. Simon was rewarded with the territory conquered from Raymond VI of Toulouse which in theory made him the most important landowner in Occitania. He became notorious and feared for his extreme cruelty, massacring whole towns, and for his “treachery, harshness, and bad faith.” In 1210 he burned 140 Cathars in the village of Minerve who refused to give up their faith. In another widely reported incident, prior to the sack of the village of Lastours, he brought prisoners from the nearby village of Bram and had their eyes gouged out and their ears, noses and lips cut off. One prisoner, left with a single good eye, led them into the village as a warning.
For that reason he is the best name bearer for a county, where people want to continue their lives where society tries to whipe them out.
Information from: http://en.wikipedia.org/wiki/Simon_de_Montfort,_5th_Earl_of_Leicester