While some Alamanni era graves have been discovered, the first mention of Herznach is in 1097 as "Hercenahc". The Ministerialis (unfree knights in the service of another lord) family von Herznach and Herznach castle are both mentioned. The castle was built on the foundations of a manor house from the 7th-10th Centuries. was built. Originally both Herznach and Ueken were ruled by the Homberger family. In the early 14th Century, the Habsburgs had the right to judge and punish theft and other felonies in Herznach. Between the Imperial Reform (1495) of Maximilian I until the fall of the Ancien Régime (1797) it belonged to the Austrian District of Rheinfelden. The rights to "Zwing und Bann" (administration of the Commons as well as low justice) were probably in the hands of the village cooperative.