Thonon-les-Bains is a town in the Haute-Savoie department in the Rhone-Alpes region in south-eastern France. It is a sub-prefecture of the department. Thonon-les-Bains was the historic capital of Chablais, a province of the old Duchy of Savoy. The Chablais Savoyard is the portion of Chablais in France. Chablais Valaison and Chablais Vaudois are those portions of Chablais in the adjacent Switzerland cantons Valais and Vaud. The town was the capital of the Dukedom of Chablais.