As early as 810 AD, Charlemagne built the Esesfeld castle in the Oldenburgskuhle, 2 kilometres from the later town, as protection against the Danes marauding from the north, but this has no direct connection with the development of Itzehoe.

Under its protection, Archbishop Ebbo of Reims built a small monastery or prayer house, the ‘Cella Lila’, in the summer of 823 in what is now Münsterdorf as a base for the Christian mission he initiated in Denmark.

The larger Echeho Castle, built around 1000 in the nearby meander of the River Stör, became the nucleus of a settlement that developed into a trading town, favoured by the granting of the Lübeck rights (1238), combined with freedom from customs duties, which at that time was only granted to Hamburg in the country, and later the right to stack goods (1260).

Itzehoe was listed as a garrison depot (Wehrkreis X (Hamburg)) of the former 225th Infantry Division, which was implicated in the 1940 Vinkt Massacre in Belgium.

Following the joint German-Soviet invasion of Poland, which started World War II in September 1939, it was the location of the Oflag X-A prisoner-of-war camp for Polish officers, which was eventually relocated to Sandbostel in 1941.

The Stör crossing (low german ‘Delf’, from which the names “Delftor” and “Delftorbrücke” of the town exit and the Störbrücke bridge originate) turned Itzehoe's castle complex into an island.

In the course of the redevelopment of the ‘Neustadt’, during which almost all the houses on this former island were demolished and replaced by new buildings and new streets were laid out, this element that characterised the town became extinct.

In order to improve the cityscape again, an initiative was launched in 2011 with the aim of promoting the reopening of the filled-in Störschleife in the centre of Itzehoe.