From the Wikipedia page 
Plzeň Region (Czech: Plzeňský kraj; German: Pilsner Region) is an administrative unit (kraj) in the western part of Bohemia in the Czech Republic. It is named after its capital Plzeň (English, German: Pilsen). In terms of area, Plzeň region is 7,561 km², the third largest region in the Czech Republic. However, the population of 572,459 inhabitants (as of 31 December 2012) it is the ninth most populous region. After the South Bohemian Region it is the second least densely populated region. The region can be roughly divided into two parts: a highly industrialized north-eastern part with a strong engineering tradition around Pilsen (Czech: Plzeň) and a more hilly and rural south-western part with smaller-sized manufacturing companies processing natural resources.
The region borders the Karlovy Vary Region (to the north-west), Ústí nad Labem Region (to the north), Central Bohemian Region (north-east), South Bohemian Region (to the east) and with Bavaria (part of Germany) in the south-west and west. The region was established based on the constitutional lax No. 347/97 of Collections concerning the formation of higher territorial administrative units. The region and its authorities are specified by Act No. 129/2000 of Collections concerning regions, which came into effect on the day of the regional authorities elections, or on January 1, 2001.