Köln-Mindener Eisenbahn-Gesellschaft
Au station was opened in August 1860 as part of the Deutz–Gießen railway by the Cologne-Minden Railway Company ("Cöln-Mindener Eisenbahn-Gesellschaft"). The Engers–Au railway ("Oberwesterwaldbahn", Upper Westerwald Railway) to Altenkirchen was opened in May 1887, connecting to Engers. Thus, it became a railway junction with an enlarged track layout.