The princes of Ostroh received the town of Tarnow as a result of the marriage of Vasyl-Kostiantyn and Sofiia Tarnovska. Initially, Sophia's brother Jan Krzysztof inherited the town. In 1567, after his death, Tarnow passed to the Ostroh principality. However, the lateral line of the Tarnow family did not accept this fact. The confrontation between the clans reached the point of military conflict. Only after the intervention of the king, Vasyl-Kostiantyn managed to return the town to his possession.
The prince rebuilt the castle, which was almost completely destroyed during the military battles, often visited it, and invited guests of the king and his retinue. In 1576, Stefan Batory visited the castle. Later, Prince Yanush Ostrozkyi lived in the castle for a long time and was even buried in the walls of the Tarnow family tomb, namely at the Tarnow church. Unfortunately, in the 18th century, Prince Yanush-Oleksandr Sangushko (who was the heir to the Ostroh estates) allowed the castle to be dismantled into building materials. Today, we can only witness the remains of the foundations.
During his lifetime, Yanush Ostrozkyi commenced building a grand memorial in the Tarnow Cathedral for himself and his first wife Suzanna Sereda. The tombstone was erected in the period from 1612 to 1624 by the architect Wilhelm van den Blocke and the sculptor Jan (Hans) Pfister.
In the center of the composition of the monument, Jan Pfister placed sculptures of Prince Yanush with his wife kneeling at the altar and asking God for the salvation of their souls. The sculptor interpreted them realistically and with great portrait resemblance. It includes many allegorical sculptures: Faith, Hope, Justice, and Courage, which reflect the virtues of Yanush and his wife and glorify the family of the Ostroh princes.
Tarnow was an iconic town for the family of the Ostroh princes. During the division of the principality between the brothers Yanush and Oleksandr, only Ostroh and Tarnow were divided in half. The other settlements were divided by the princes without tearing them into pieces.