Rorschach is a municipality, in the District of Rorschach in the canton of St. Gallen in Switzerland. It is on the south side of Lake Constance. …Rorschach is a municipality, in the District of Rorschach in the canton of St. Gallen in Switzerland. It is on the south side of Lake Constance. Rorschach is first mentioned in 850 as Rorscachun. In 947, Otto I granted the abbot of St. Gall the right to operate markets, mint coins and levy tariffs at Rorschach.