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Cognomen Janssen (Janssen , 楊森 , Янссен ) , in the world, is a widespread last name. The family name Janssen is characteristic of Netherlands, where it is a common surname, Belgium, where it is quite a common surname, and Aruba (explore the name in all countries). Not in comparison with a country's population, it most frequently occurs in Netherlands, Germany, and the United States. Much less frequently, Janssen is the forename as well as the last name.