The Zasławski family had its power base in Volhynia, Crown of the Kingdom of Poland (today in Ukraine), and traced its origins to a branch of the Rurikids that took its name from the Iziaslav.

Due to their relation to the Rurikids, the Zasławski family held the title of Knyaz (prince).

After the death in 1620 of the last male heir of the Ostrogoski family, Janusz Ostrogski, many of the Ostrogoski possessions were inherited by the Zasławcy.

Their huge possessions passed to the Lubomirski family (due to their marriage with Aleksander's sister, Teofilia Ludwika Zasławska) and other families of Polish szlachta.

A complicated litigation concerning the Ostrogski inheritance continued until the Russian Empire annexed Poland during the Partitions.