The history of Chmielnik dates back to the 11th century, but it became famous in 1241 when Chmielnik was the place of a battle with the Tartars - one of the largest battles of 12th-century Europe. An obelisk that commemorates this event is placed next to the Chmielnik-Szydłów road. Chmielnik belonged to Polish dukes and was subject to the castellany of Sandomierz, in the 12th century it became the property of the Odrowąż family. During the Tartar invasions Chmielnik was owned by the Oleśnicki family and in 1551 it was granted a royal charter by King Sigismund Augustus. Since Jan Oleśnicki, the town owner, was a zealous supporter of the Reformation who wished to establish a Protestant community in Chmielnik, he had the local church of the Holy Trinity defiled and gave it to the Protestants. At the beginning of the 17th century Chmielnik changed its owners and became the property of the Gołuchowski family. During the Reformation Chmielnik was - like many other local towns - a centre of the Arians and hosted Calvin synods. In the years 1634-1636 a new Protestant church was built, it was burned during the Polish-Swedish war in the years 1650-1655. The Protestant community itself existed in Chmielnik until 1689. The next owner was Andrzej Moszczyński, the governor of the Inowrocław Province. In the years 1787-1829 Chmielnik belonged to the Chłapowski family. Dezydery Chłapowski - the last representative of the Chłapowski family - sold the town to the Tański family, which owned Chmielnik until the end of World War II. The tragic events of World War II changed the life of this small town for ever. Chmielnik suffered great losses of its population. On 13 January 1945 the Red Army liberated Chmielnik from the German occupation and on 4 February 1945 the Town National Council was established. By the end of 1998, prior to carrying out the administrative reform, the commune was in the boundaries of the Kieleckie Province.
Before the outbreak of World War II, the population of Chmielnik was nearly 9 000. In 1942 the population rose to over 15 000, as a result of the resettlements of the Poles from the western areas of Poland and displacements of the Jews. Out of this population, the Germans expelled over 11 000 people on 6 October 1942 and later till January 1943. During the relocations about 200 Jews were killed on the spot. The number of victims among the Polish population was over 70.