Ostroh is a city in Rivne Oblast, western Ukraine. It is situated on the Horyn River. Ostroh was the administrative center of Ostroh Raion u…Ostroh is a city in Rivne Oblast, western Ukraine. It is situated on the Horyn River. Ostroh was the administrative center of Ostroh Raion until 2020, but as a city of oblast significance did not belong to the raion. Currently the city is the centre of Ostroh urban hromada. Population: 14,894.