During the [[Khmelnytsky Uprising]], the town was burned by the [[Cossack]]s, and its residents were murdered. Ostrog slowly recovered, and in the second half of the 18th century, it became the seat of a Jesuit college (see [[Collegium Nobilium (Warsaw)|]]). In 1793, the town was annexed by the [[Russian Empire]], in which it remained until 1918. Railroad lines, built in the 19th century, missed Ostrog, and as a result, the town stagnated.
In the interbellum period, Ostrog belonged to County of [[Zdolbunow]], of the [[Second Polish Republic]]. The town was an important garrison of the [[Polish Army]], and the [[Border Protection Corps]] (KOP). Here, KOP Battalion “Ostrog” was stationed, as well as the 19th Regiment of Volhynian [[Uhlan]]s. On July 7, 1920, during the [[Polish-Soviet War]], a battle between Polish unit under Wincenty Krajowski, and Bolsheviks of [[Semyon Budyonny]]’s [[1st Cavalry Army]] took place. Since in 1919 - 1939 Ostrog was located in close proximity to the Polish - Soviet border, special passes were required to enter some districts of the town.