Jan of Tarnow founded the town of «Tarnopol» on April 15, 1540. After, locals have verbally adapted «Tarnopol» and renamed it to Ternopil.

The daughter of Hetman Jan of Tarnow Sophia of Tarnow got married to Prince Vasyl-Kostiantyn Ostrozkyi. She died early (she died during the birth of her youngest son Oleksandr), but survived her older brothers. That is why she became the heir to all paternal possessions and brought Ternopil to the possessions of the princes of Ostroh.

Together with the town, Prince Vasyl-Kostiantyn inherited the castle of Hetman of Tarnow. He rebuilt it, but today the remains of the former castle have only survived in the lower part of the modern city council. 

In the year of his wife’s death (1570), Prince Vasyl-Kostiantyn Ostrozkyi created a fund for the hospital at the Church of the Nativity in her memory, giving it about 140 hectares of arable land near the town and acquired several surrounding buildings next to the church. The hospital cared for and supported poor and infirm Orthodox people.