Cieszyn Silesia, Těšín Silesia or Teschen Silesia ( ; or ; or ) is a historical region in south-eastern Silesia, centered on the towns of Cieszyn and Český Těšín 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. The historical boundaries of the region are roughly the same as those of the former independent Duchy of Teschen/Cieszyn. Currently, over half of Cieszyn Silesia forms one of the euroregions, the Cieszyn Silesia Euroregion, with the rest of it belonging to Euroregion Beskydy. Administrative division From an administrative point of view, the Polish part of Cieszyn Silesia lies within the Silesian Voivodeship and comprises Cieszyn County, the western part of Bielsko County, and the western part of the town of Bielsko-Biała. The Czech part lies within the Moravian-Silesian Region and comprises the Karviná District, the eastern part of the Frýdek-Místek District, and the eastern parts of the Ostrava-City District and of the city of Ostrava itself. History Cieszyn Silesia covers the area of the former Duchy of Teschen, which existed from 1290 to 1918. Before 1290 the area constituted a castellany, which together with Castellany of Racibórz formed the Duchy of Racibórz in 1172. From 1202 it was a part of the united Duchy of Opole and Racibórz. From 1290 to 1653 the Duchy of Teschen was ruled by the local branch of the Piast dynasty. In 1327 Casimir I, Duke of Cieszyn, swore homage to the Bohemian king John of Bohemia, and the duchy became an autonomous fiefdom of the Kingdom of Bohemia and later the Bohemian Crown. Piast rule continued until 1653 and the death of the last Piast descendant, Elizabeth Lucretia, Duchess of Cieszyn, after which it lapsed directly to the Kings of Bohemia, at that time from the Habsburg dynasty. From 1722, the dukes of Teschen hailed from the Dukes of Lorraine dynasty, from 1767 to 1822 from the Wettin dynasty, and from 1822 to 1918 from the Habsburg-Lorraine dynasty. Cieszyn Silesia was cemented as a uniform historic, geopolitical, socio-cultural and economic entity during the period of Habsburg rule. It is distinct from the rest of Silesia because after the First Silesian War between the Habsburg Monarchy and Prussia it remained part