Several Polish kings and notables visited the town, but following the catastrophic Swedish Deluge (1655–1660), Wieluń declined and never regained its status.

Jan Długosz wrote that Wieluń was located in the area abundant with water, which may mean that the former theory is correct.

It was based on the medieval Castellany of Ruda (located some 4 km (2 mi) from Wieluń), which was established in the 10th or 11th century.

The Castellany of Ruda was first mentioned in the 1136 Bull of Gniezno, and during the period known as Fragmentation of Poland (see Testament of Bolesław III Wrymouth), it was part of the Seniorate Province.

In the mid-14th century King Casimir III the Great built a castle here, which was part of defensive system protecting the border between the Kingdom of Poland and Czech-ruled Silesia.

In 1370, following the last will of Casimir the Great, King Louis I of Hungary handed the Land of Wieluń to Duke of Opole, Władysław Opolczyk.

At the beginning of the 17th century, the mother of future Grand Crown Hetman Stanisław Koniecpolski, one of the greatest commanders in Polish history, founded a Renaissance monastery of the Bernardine nuns in Wieluń, now housing a museum dedicated to the town's history.

After World War I, Poland regained independence in 1918, and in the interbellum Wieluń was a county seat in the Łódź Voivodeship.

On 1 September 1939, the city was bombed by the German Luftwaffe in the first action of World War II (apart from the Jabłonków Incident on 25/26 August).

In the Bombing of Wieluń, German planes destroyed most of the town centre, including a clearly marked hospital, a synagogue, and the historic Gothic church, and killed at least 127 civilians.

[6] On 6–8 September 1939 the Einsatzgruppe II entered the town, and mass searches of Polish offices and organizations were carried out.

The Germans instigated a reign of terror against the Jewish population of Wieluń, which had lived there since the 1500s and amounted to around 4,000 people at the beginning of the war.

[10] During the German occupation, a transit camp was operated in the town for Poles expelled from the region, who were then either deported to the so-called General Government in the eastern part of German-occupied Poland or to forced labour in Germany and German-occupied France or sent as slave laborers to new German colonists in the town's vicinity.

Later that year, the 2,000 Jews still remaining in the city and others brought to Wieluń were rounded up and confined for several days in a church building without food or water.

[3] Displayed artifacts include jewelry and weaponry from the Bronze Age and Middle Ages, weapons and memorabilia from the 19th-century Polish national liberation uprisings, religious paintings and traditional folk sculptures, and Biblia Brzeska, one of the oldest Polish translations of the Bible.

[3] There are monuments to notable people such as Witold Pilecki and Pope John Paul II in Wieluń.

The biggest communication problem in Wieluń is huge traffic (including transit) in the center of the town, due to lack of bypasses.

The line was built in the 1920s, as the junction of Kluczbork remained within borders of Weimar Germany and direct rail communication between Polish part of Upper Silesia and Poznań was impossible.

Wieluń is directly connected by rail with such cities as Tarnowskie Góry, Katowice, Poznań, Szczecin and Kępno.

In the past, WKS Wieluń had several departments, such as track and field, basketball, table tennis, handball and association football.

Another notable club is Siatkarz Wieluń [pl], volleyball team, which competes in the lower leagues, but in the past played in the PlusLiga, Poland's top division, most recently in the 2010–11 season.