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Last name Klaass (Klaass ) , throughout the world, is a very rare cognomen. The cognomen Klaass is habitual in Austria, where it is a rare surname, Germany, where it is a very rare surname, and Italy, where it is an extremely rare surname. Measured by absolute frequency, it most frequently occurs in Germany, Austria, and the United States. Much less frequently, Klaass is the forename as well as the last name.