As per the 28 July 1920 decision of the Spa Conference the areas assigned to the Těšín electoral district were divided between Czechoslovakia and Poland. The area awarded to Czechoslovakia covered 1269 km2 and some 285,000 inhabitants, the area awarded to Poland constituted 1,013 km2. with some 150,000 inhabitants. The district centre, Těšín, was divided into two by the Olza river.