 Nyorai kuenderera kweiyi ndima - Kubva muna 1356 Oster yaive pasi pekutonga kweGreat Duchy yeLithuania, uye kubva muna 1569, pasi peUnion yeLublin, yaive chikamu chePolish-Lithuanian Commonwealth. Muna 1648 yakava chikamu uyezd county of the Pereiaslav regiment. Kubvira muna 1654, Oster yakanga yava kutongwa neUmambo hweRussia. Muna 1622, Mambo Jan II Casimir akapa Oster kodzero dzeMagdeburg nechidzitiro chezvombo. Pashure pehondo dzinotyisa dzeHondo yeUkraine yeRusunungukoMuna 1664, kutonga kwePoland kwakagadzwa zvakare muOster, asi muna Kukadzi 1664, nerutsigiro kubva kuvanhu vemuno, maPoland akadzoserwa nemaCossacks nemaRussia. Muna 1803, guta racho rakava uyezd centre yeChernigov Gubernia. 