The first source information about a fortified settlement Kosle comes from the Gall Anonim’s Chronicle (written in the years 1112-1116). The settlement must have existed earlier, as in 1106 it was destroyed by a fire. The town’s favourable location at the intersection of the trade routes from Prague and Opawa to Bytom, Wrocław and Kraków positively influenced its economic development. Around 1281, Koźle was granted town rights under the German law. The following villages developed in the neighbourhood: Kędzierzyn (founded in 1283), Kłodnica (founded in 1303) and Sławięcice (founded in 1245, gained temporary town rights in 1260). In the 1280s, the Duchy of Opole was divided and Koźle with the neighbouring villages became part of the Duchy of Bytom and Koźle.
In 1327, Duke Władysław from Bytom paid a liege homage to the King of Bohemia, and as a result Koźle passed under Czech rule and shared the political fate of Silesia. In 1526, the King of Bohemia and Hungary Ludwik II Jagiellończyk died without an heir, and as a consequence the Austrian Archduke Ferdinand Habsburg succeeded to the throne of Bohemia. After the death of Jan II Dobry, the last duke of the Piast dynasty, the land of Koźle became part of the Habsburg monarchy in 1532. During the Thirty Years’ War (1618-1648), in 1642, the Swedish army invaded and completely destroyed Koźle, which was not able to recover from the economic downfall until the 18th century. In 1741, during the War of the Austrian Succession, the Prussian army occupied Koźle, which was subsequently incorporated into Prussia in 1742. The town’s name was changed to Cosel and almost immediately the construction of big defence fortifications began, which created the Cosel Fortress. In 1787, there were 1,710 inhabitants and 1,300 military men in the town.
In the years 1792-1821, the Kłodnicki Canal was built, which connected the Odra River (in the area of Koźle) with the industrial district of Zabrze and Gliwice. The construction of the canal stimulated the economic development of the nearby villages, above all that of Sławięcice and Blachownia. In 1807, the Cosel fortress was besieged in vain by Napoleon’s Army. From 1819, the Koźle county belonged to the Regierungsbezirk Poland in Silesia Province of Prussia.
The year 1846 was the turning point in the history of the whole region. It was then that the railway station in the village Kędzierzyn was built, by the new railway line connecting Wroclaw with Gliwice and Raciborz. From this moment on, Kędzierzyn began to develop quickly, whereas Koźle came to a standstill, as its development was blocked by the fortifications. Even the decision to liquidate the fortress in Koźle in 1873 and the construction of a river harbour on the Odra River did not change the situation. In 1910, the number of inhabitants in Koźle amounted to 7,800, in Kędzierzyn – 4,000 and in Kłodnica - 3,700.
In 1921, the territory of Kędzierzyn was the site of Polish-German fights during the Third Silesian Uprising, but after a referendum the territories were acknowledged to Germany (as only 25% of the inhabitants voted for Poland). The big crisis of 1929-1933 strongly affected local industry. After the national socialists had come to power in Germany, a plan to fight unemployment was implemented, which included building the new Gliwice Canal in 1934-1938, connecting the Koźle harbour with Gliwice. In 1939, the population of Koźle increased to 13,300 inhabitants, the of Kędzierzyn to 6,300 and the of Kłodnica to 4,900.
During World War II, in 1939, the German group Oberschlesische Hydriewerke A.G. began the construction of a chemical plant in Blachownia, and from 1940 the group Interessen-Gemeinschaft Farbenindustrie AG started the construction of a plant in Azoty. The plants were supposed to produce airplane and rocket fuel for the needs of the German air force. As labour was required for the plants construction works, and subsequently for production in the plants, the Germans created a network of more than 40 forced labour camps in the region of Kędzierzyn, where they brought about 35,000 prisoners of different nationalities. In 1944, the American air force operating from their air base in Italy, carried out a carpet bombing of the industrial plants of the region.
The destroyed chemical installation was taken to the Soviet Union after the war. In 1945, the town was incorporated into Poland. Polish settlers from Kresy (Eastern Borderlands) and central provinces took place of the resettled German population. The nationality of majority of the Silesian population was verified successfully and they received Polish citizenship. In the years 1950-1975, the Koźle county belonged to Opole Province (as well as after the administration reform in 1999). In 1951, Kędzierzyn was granted town rights. The Kędzierzyński Canal, joining the Odra River with the nitric plants was opened in 1970. In 1975, one town Kędzierzyn-Koźle was formed from the unification of Kędzierzyn, Koźle, Kłodnica and Sławięcice.
- Monografia Miasta Kędzierzyn-Koźle, E. Nycz, S. Senft (eds.), Opole (2001).
- Ziemia kozielska, S. Popiołek (ed.), Koźle (1963).