Cognomen Bylyn (Bylyn 
, Билин 
, Былин 
) , all around the world, is a rare last name. The cognomen Bylyn is characteristic of Kazakhstan, where it is a rare surname, Kyrgyzstan, and Belarus. In absolute terms, it is the most numerous in Russia, Kazakhstan, and Kyrgyzstan. Much less frequently, Bylyn is the forename as well as the last name.