Oster district was the inner district in Volynia governorate. It bordered Dubno and Kremenets districts on the West, Rovno district on the north, Zaslavl district on the east and Starokonstantinov district on the south.
| Place | Record |
|---|---|
| Otsrog | |
| Goshcha | Auguts 1816: artisans, bourgeois |
| Kilikiev | August 1816 |
| Lakhovtsy (Belogorie) | August 1816: artisans, bourgeois |
| Mezhirichi | August 1816 |