The medieval gord in Ciechanów numbered approximately 3,000 armed men,[2] and together with the region of Mazovia, it became part of the emerging Polish state in the late 10th century.

In 1254, Ciechanów is mentioned as the seat of a castellany (Rethiborius Castellanus de Techanow (Racibor, Kasztelan Ciechanowa)).

In the Middle Ages, the defensive gord of Ciechanów protected northern Mazovia from raids of Lithuanians, Yotvingians, Old Prussians and later, the Teutonic Knights.

This must have happened before 1475, as a document from that year, issued by Duke Janusz II of Warsaw, states that Ciechanów has a Chełmno town charter.

During the Polish–Soviet War, in 1920, the town was briefly occupied by the Soviet Russians, who resorted to rape and looting of stores, houses and schools.

[6] The one remaining Catholic priest was harassed by the occupiers, however, thanks to the intercession of the local population, he avoided deportation or death.

[8] Some local socialists and intelligentsia joined the occupation structures for diversionary purposes, and when the Polish army reached the city again on August 15, 1920, they immediately disarmed several hundred Soviets.

The vast majority of the Polish and Jewish population was seen as racially inferior and Germany planned its eventual annihilation.

[11] The Germans carried out mass searches of Polish and Jewish homes, offices and organizations, as well as synagogues, which were desecrated and looted.

[12] Several hundred Poles were transported from the jail in Ciechanów and murdered in large massacres in the nearby village of Ościsłowo as part of Intelligenzaktion.

[18] Before World War II, Ciechanów was home to a large Jewish community of 1,800, but during the Nazi German occupation, in November 1942, the majority of the Jewish community were transported to the Red Forest (Czerwony Bór) northeast of town and murdered in a mass shooting.

On January 17, 1945, Ciechanów was captured from Nazi Germany by the Red Army, and was restored to Poland after the war.