Herzhorn was an Amt ("collective municipality") in the district of Steinburg, in Schleswig-Holstein, Germany. The seat of the Amt was in Herzhorn. In January 2008, it was merged with the Amt Horst to form the Amt Horst-Herzhorn.
The Amt Herzhorn consisted of the following municipalities: Blomesche Wildnis Borsfleth Engelbrechtsche Wildnis Herzhorn Kollmar Krempdorf Neuendorf bei Elmshorn