As a result of German colonization, the town became German-speaking, putting Slavic speakers at disadvantage.
In 1516 local Germans enforced a ban on buying goods from Slavic speakers.
It was also forbidden to accept native Slavs to craft guilds, which indicates ethnic discrimination.

In 1531 riots took place between supporters and opponents of the Protestant Reformation.
In 1534 the city became mostly Lutheran under the influence of Johannes Bugenhagen.
In 1568, John Frederick, Duke of Pomerania and bishop of Cammin, started constructing a residence, finished by his successor Casimir VI of Pomerania in 1582.
After the 1637 death of the last Pomeranian duke, Bogislaw XIV, the city passed to his cousin, Bishop Ernst Bogislaw von Croÿ of Kammin.
Occupied by Swedish troops during the Thirty Years' War in 1637, some of the city's inhabitants sought refuge in nearby Poland.
The city was granted to Brandenburg-Prussia after the Treaty of Westphalia (1648) and the Treaty of Stettin (1653), and with all of Farther Pomerania became part of the Brandenburgian Pomerania.

As part of the Kingdom of Prussia, "Cöslin" was heavily damaged by a fire in 1718, but was rebuilt in the following years.
In 1764 on the Chełmska Hill, now located within the city limits, a Pole Jan Gelczewski founded a paper mill that supplied numerous city offices.
The city was occupied by French troops in 1807 after the War of the Fourth Coalition.
Following the Napoleonic wars, it became the capital of Fürstenthum District (county) and Regierungsbezirk Cöslin (government region) within the Province of Pomerania.
The Fürstenthum District was dissolved on 1 September 1872 and replaced with the Cöslin District on December 13.
Between 1829 and 1845, a road connecting Koszalin with Szczecin and Gdańsk was built.
Part of this road, from Koszalin to the nearby town of Sianów, was built in 1833 by around one hundred former Polish insurgents.

The town became part of the German Empire in 1871 during the unification of Germany.
The railroad from Stettin (Szczecin) through "Cöslin" and Stolp (Słupsk) to Danzig (Gdańsk) was constructed from 1858–78.
A military cadet school created by Frederick the Great in 1776 was moved from Kulm (Chełmno) to the city in 1890.

After the Nazi Party took power in Germany in 1933, a Gestapo station was established in the city and mass arrests of Nazi opponents were carried out.
After the Nazis had closed down Dietrich Bonhoeffer's seminar in Finkenwalde (a suburb of Stettin, now Szczecin) in 1937, Bonhoeffer chose the town as one of the sites where he illegally continued to educate vicars of the Confessing Church.
During the Second World War Köslin was the site of the first school for the "rocket troops" created on orders of Walter Dornberger, the Wehrmacht's head of the V-2 design and development program.
The Nazis brought many prisoners of war and forced labourers to the city, mainly Poles, but also Italians and French.
A labour camp of the Stalag II-B POW camp was located in the city.
After crushing the Warsaw Uprising, the Germans brought several transports of Poles from Warsaw to the city, mainly women and children.
As a result of German colonization, the town became German-speaking, putting Slavic speakers at disadvantage. In 1516 local Germans enforced a ban on buying goods from Slavic speakers. It was also forbidden to accept native Slavs to craft guilds, which indicates ethnic discrimination.
In 1531 riots took place between supporters and opponents of the Protestant Reformation. In 1534 the city became mostly Lutheran under the influence of Johannes Bugenhagen. In 1568, John Frederick, Duke of Pomerania and bishop of Cammin, started constructing a residence, finished by his successor Casimir VI of Pomerania in 1582. After the 1637 death of the last Pomeranian duke, Bogislaw XIV, the city passed to his cousin, Bishop Ernst Bogislaw von Croÿ of Kammin. Occupied by Swedish troops during the Thirty Years' War in 1637, some of the city's inhabitants sought refuge in nearby Poland. The city was granted to Brandenburg-Prussia after the Treaty of Westphalia (1648) and the Treaty of Stettin (1653), and with all of Farther Pomerania became part of the Brandenburgian Pomerania.
As part of the Kingdom of Prussia, "Cöslin" was heavily damaged by a fire in 1718, but was rebuilt in the following years. In 1764 on the Chełmska Hill, now located within the city limits, a Pole Jan Gelczewski founded a paper mill that supplied numerous city offices. The city was occupied by French troops in 1807 after the War of the Fourth Coalition. Following the Napoleonic wars, it became the capital of Fürstenthum District (county) and Regierungsbezirk Cöslin (government region) within the Province of Pomerania. The Fürstenthum District was dissolved on 1 September 1872 and replaced with the Cöslin District on December 13. Between 1829 and 1845, a road connecting Koszalin with Szczecin and Gdańsk was built. Part of this road, from Koszalin to the nearby town of Sianów, was built in 1833 by around one hundred former Polish insurgents.
The town became part of the German Empire in 1871 during the unification of Germany. The railroad from Stettin (Szczecin) through "Cöslin" and Stolp (Słupsk) to Danzig (Gdańsk) was constructed from 1858–78. A military cadet school created by Frederick the Great in 1776 was moved from Kulm (Chełmno) to the city in 1890.
After the Nazi Party took power in Germany in 1933, a Gestapo station was established in the city and mass arrests of Nazi opponents were carried out. After the Nazis had closed down Dietrich Bonhoeffer's seminar in Finkenwalde (a suburb of Stettin, now Szczecin) in 1937, Bonhoeffer chose the town as one of the sites where he illegally continued to educate vicars of the Confessing Church. During the Second World War Köslin was the site of the first school for the "rocket troops" created on orders of Walter Dornberger, the Wehrmacht's head of the V-2 design and development program. The Nazis brought many prisoners of war and forced labourers to the city, mainly Poles, but also Italians and French. A labour camp of the Stalag II-B POW camp was located in the city. After crushing the Warsaw Uprising, the Germans brought several transports of Poles from Warsaw to the city, mainly women and children.
Koszalin