Wielun ['vj?lu?] (German: Welun) is a city in central Poland with 24,347 inhabitants (2006). Situated in the Lódz Voivodeship (since 1999), it was previously in Sieradz Voivodeship (1975–1998). Wielun has a long and rich history. In the past, it used to be one of the most important urban locations of the Kingdom of Poland, and the capital of the Land of Wielun (Ziemia wielunska). Several Polish kings and notables visited the town, but following the catastrophic Swedish invasion of Poland (1655–1660), Wielun declined and never regained its status. In September 1939, during the Invasion of Poland, it was bombed by the Luftwaffe. The Bombing of Wielun is considered to be one of the first bombings in Europe in this war. It killed an estimated 1,300 civilians, injured hundreds more and destroyed 90 percent of the town centre.

Wielun is an important road junction, the town also has a sports club WKS Wielun, established in 1957 after a merger of two earlier clubs. In the past, WKS Wielun had several departments, such as track and field, basketball, table tennis, handball and association football. Currently, the only remaining department is football.