Chełmno (older ; ) is a town in northern Poland near the Vistula river with 20,000 inhabitants and the historical capital of Chełmno Land. Situated in the Kuyavian-Pomeranian Voivodeship since 1999, Chełmno was previously in Toruń Voivodeship (1975–1998).
The first written mention of Chełmno is known from a document allegedly issued in 1065 by Duke Boleslaus II of Poland for the Benedictine monastery in Mogilno. In 1226 Duke Konrad I of Masovia invited the Teutonic Knights to Chełmno Land. In 1233 Kulm was granted city rights known as "Kulm law" (renewed in 1251), the model system for over 200 Polish towns. The town grew prosperous as a member of the mercantile Hanseatic League. Kulm and Chelmno Land were part of the Teutonic Knights' state until 1466, when after the Thirteen Years' War Chełmno was incorporated into Poland and made the capital of Chełmno Voivodeship.
In 1772, following the First Partition of Poland-Lithuania, the city was taken over by the Kingdom of Prussia. Between 1807 and 1815 Chełmno was part of the Duchy of Warsaw, being reannexed by Prussia at the end of the Napoleonic Wars.
Kulm had been a garrison town. In 1776 Frederic the Great founded here a cadet school which was to serve in Germanising Polish areas and nobility In 1890 the garrison included 561 military staff. On 1 October 1890 the cadet school was moved to Köslin in Farther Pomerania.
Chełmno returned to Poland in 1920 following World War I.
When World War II broke out in 1939, Nazi German authorities murdered 5,000 Polish civilians upon taking control of the territory. The atrocities took place in Klamry, Małe Czyste, Podwiesk, Plutowo, Dąbrowa Chełmińska, and Wielkie Łunawy, while many other Poles were executed in forests. The rest of the Polish population was expelled to the General Government in line with the German policy of Lebensraum. Polish Secret State resistance groups such as Polska Żyje ("Poland Lives"), Rota, Grunwald, and Szare Szeregi were also active in the area. The area was administered as part of Reichsgau Danzig-West Prussia and served as the seat of the district/county (kreis) of Kulm.
On 25 January 1945 German forces set fire to several buildings in the city, including a hospital, a railway terminal, and a brewery, while retreating (see scorched earth).