Until the mid 19th century the town lay within the estate of Krasiński family. The Jews, who began settle there since mid 18th century, made up 60% of its population by 1841. The Jewish district was defined by a legal document according to which, they were obliged to pay rent to count Józef Krasiński. A Jewish kahal was established in Krasnosielc in 1844 following official complaint about improprieties of the kahal in Przasnysz. Krasnosielc lost its municipal status in 1869 soon after its last Polish owner Karol Krasiński died childless. In 1883 a synagogue was built. The town changed hands several times before Poland regained its independence in 1918.
The Jewish community of Krasnosielc ceased to exist in early September 1939. Following German invasion of Poland, SS units of Panzer Division Kempf forced the Jews into the Synagogue and massacred them there. A day later, the remainder (mostly men) were machine-gunned at the same location. The anti-Jewish massacre became widely publicized in Berlin as the first of its kind on Polish soil. The perpetrators received sentences of a few years, and their superiors were replaced.