The official names of towns in Europe changed when regions were conquered and new rulers took over. Additionally, Jews often gave their towns Yiddish names. For example, the town in czarist Russia where Grand Rabbi Israel Korff once lived was under Polish rule in the 1200s, it became part of the combined kingdom of Lithuania and Poland in the 1300s. In 1772, the Russians under the czarist regime took dominion. Eventually in the early 1920s the Soviets took control after the overthrow of the czar and the civil war that followed. Germany seized control during the Holocaust but the Soviets eventually defeated them. In 1991, Ukraine declared its independence from the USSR in 1991 and the town now belongs to Ukraine.
The Jews called the town Zvil. (Among the alternate spellings for Zvil are Zviagel, Zvihil, Zwiahl, and Zwehil.) The official name of the town at the time Rabbi Korff made his home there was Novograd Volynsk but is now Novograd Volynskiy.
The town where Grand Rabbi Jacob Korff was believed to be born was Medzhibozh, also spelled Medzibov, Medzibozh, Medzebozh,Mezbez, Medzibezh, Miedzyboz, Smiedzyborz.
For a comprehension study on places names see Where Once We Walked: A Guide to the Jewish Communities Destroyed in the Holocaust by Gary Mokotoff and Sallyann Amdur Sack (Teaneck, NJ: Avotaynu, Inc., 1991).