Family name Casimirus (Казимир 
, Casimirus 
) , across the world, is quite a rare cognomen. The last name Casimirus is habitual in Eastern Europe, particularly Ukraine, where it is a rare surname, Belarus, and Russia. Not in comparison with a country's population, it is the most numerous in Russia, Ukraine, and Kazakhstan. More frequently, Casimirus is the forename as well as the last name.