The town of Polonne has been known since the times of Kyivan Rus, but it came into the possession of the Ostroh princes only in 1494. The Grand Duke of Lithuania Alexander Jagiellon handed over the town to Prince Kostiantyn Ivanovych Ostrozkyi. However, the prosperity of the town got under way only after Polonne was passed to the possession of Prince Vasyl-Kostiantyn Ostrozkyi. The prince erected a wooden castle over stone foundations in Polonne. Some walls may have been made of brick, but the description of the first third of the 17th century mentions only wooden structures.
A brick church of the Assumption of the Blessed Virgin Mary was built on the territory of the castle. Its construction got started in 1593 by Prince Yanush Ostrozkyi. The church was probably built in place of a wooden church. On the 20th of January 1602, the wedding of the Prince’s Yanush daughter Eleonora to Hieronymus Yazlovetskyi took place at the shrine. Traditionally, historians suggest that the church was constructed in 1607, though, apparently, it was some kind of extension to the existing church.
An interesting fact that in the spring of 1603 the owner of Polonne became Yanush's younger brother Oleksandr, who was of the Orthodox faith and did not get on well with his older brother. Yet, Oleksandr possessed town not for a while – he died at the age of 33 in December of that year. The junior prince set out last his journey right from Polonne.
Shortly before his death, the prince managed to grant the inhabitants of the town a privilege exempting them from taxes for 20 years. After Oleksandr’s death, the town was inherited by his daughter Sophia and brought as a dowry to the Liubomyrski family.