The first Jewish settlers appeared in Koźmin in 1500. It was a group of 20 people who established the local Jewish community at the beginning of the 16th century. By 1622, the Jewish population of the town had grown significantly. Jews lived in a separate district located inside the city walls. At first, they worked as middlemen, tenants, and inn-keepers, but as the time passed, Jewish house owners and craftsmen started to appear in the town. Jewish market stalls were situated at the marketplace, in the vicinity of the castle, and in front of the church. In 1674, Koźmin had a population of 535, including 37 Jews (6.5% of the population).

On 30 June 1715, the town owner, Jan Kazimierz Sapieha, granted the Jewish people a privilege allowing them to build a synagogue, a cemetery, a mikveh, and houses for the rabbi and the teacher. The privilege also confirmed their right to conduct business activity in the town. These changes attracted many new Jewish settlers in Koźmin. The privilege was confirmed by the subsequent owner of the town, Jan Kanty Sapieha, on 27 August 1753.

In 1776, the Jewish community had 148 members. In 1793, when it was incorporated into Prussia following the Second Partition of Poland, Koźmin had a population of 1,513, including ca. 300 Jews. The fire which ravaged the town on 9–10 September 1797 destroyed a large part of the Jewish district – ca. 14 houses with outbuildings. At the beginning of the 19th century, ca. 350 Jewish people lived in Koźmin.

According to preserved data, the Jewish community had 301 members (64 families) in 1815. It owned a wooden synagogue and a school. In 1835, the Jewish population increased to 670 people, and reached 722 people in 1840. The size of the community reached its peak in 1856 with 863 people (24% of the population). The same period marked growing influence of Jews in the local public life. At the turn of the 20th century, representatives of the kehilla were granted seats on the Municipal Council. One of them, a man called Kantorowicz, was even the council’s chairman. However, the number of Jews living in the town soon began to fall (primarily due to emigration to inner Germany and the USA). In 1941, Koźmin had 270 Jewish residents among a total population of ca. 5,000 people.

After World War I, the size of the Jewish population in Koźmin decreased even further. In 1923, there were only 48 Jews in the town, mostly craftsmen and shop owners. There was also a Jewish photographer (Sonnefeld), lawyer (Feliks Łączewski), and brickyard owner (Egon Schleyer). Despite its small size, the community still owned a synagogue, two houses, and a cemetery. However, no rabbi was employed, with the rabbi from Kepno occasionally commuting to Koźmin.

At the outbreak of World War II, only 33 Jewish people lived in Koźmin. The town was seized by Germans on 6 September 1939. The Nazis confiscated Jewish property and closed the synagogue. On 2 November 1939, all local Jewish people were arrested and transported to the ghetto in Łódź. Almost all of them died in death camps. The only survivors were Nathan Mośkiewicz and his son Hugon. The former returned to Koźmin after the war and died there in 1969. He was buried at the local Jewish cemetery.