[5] In 1331, during the Polish–Teutonic War, the Teutonic Knights plundered and destroyed the town, and murdered its defenders.

A painting picturing the battle can be seen in the museum at the current Home of the Swedish royal family Drottningholm Palace near Stockholm, Sweden.

During the German Invasion of Poland, which started World War II, the Wehrmacht reached Kłecko on 8 September 1939 and a battle was fought in which the town was fiercely defended by Poles.

[8] The commanders of the Polish defense were captured by the Germans in October 1939, and then murdered in November 1939.

Edward Paulus, founder of the local unit of the Union of Armed Struggle, was arrested by the Gestapo in 1942, and eventually sentenced to death and executed the following year.