Bielsko [ˈbjɛlskɔ] (German: Bielitz, Czech: Bílsko) was until 1950 an independent town situated in Cieszyn Silesia, Poland. In 1951 it was joined with Biała Krakowska to form the new town of Bielsko-Biała. Bielsko constitutes the western part of that town.Bielsko was founded by the Cieszyn Piast dukes in the late 13th century on the grounds of village later called Stare Bielsko (Old Bielsko), on the Biała River. It was first mentioned in a written document in 1312.