Cieszyn Silesia or
Tešín Silesia or
Teschen Silesia (
Polish: ,
Czech: or ,
German:
Teschener Schlesien or
Olsagebiet) is a historical region in south-eastern
Silesia, centered on the towns of
Cieszyn and
Ceský Tešín and bisected by the
Olza River. Since 1920 it has been divided between
Poland and
Czechoslovakia, and later the
Czech Republic. It covers an area of about and has about 810,000 inhabitants, of which (44%) is in Poland, while (56%) is in the Czech Republic.