Kostopil

Kostopil developed from the village of Ostaltsi on the Zamchyske River, a tributary of the Horyn in Volhynia. Great and Little Ostaltsi appear in registers of 1648–1658 as property of the Zaslavsky princes. The later town therefore grew within an existing estate landscape rather than beginning on unoccupied land. In 1783 Leonard Worcell obtained a privilege from King Stanisław August Poniatowski to establish a town there under the name Kostopil.

The new town was still small when the partitions changed its sovereign. It passed to the Russian Empire in the Second Partition of Poland in 1793. Initially administered within the Iziaslav vicegerency, it became part of Rivne district in Volhynia Governorate in 1797. The following year it contained thirty households and 248 inhabitants. These records describe a modest settlement, a royal town foundation set beside a much older village.