Vallée de l'Ernz is a commune in northern Luxembourg, in the canton of Diekirch. The commune of Vallée de l'Ernz was formed on 1 January 2012 from the former communes of Ermsdorf and Medernach. The law creating Vallée de l'Ernz was passed on 24 May 2011. It has an area of 39.73 km2.