The Masurians or Mazurs (Polish: Mazurzy, German: Masuren, Masurian: Mazurÿ) are a small 5,000-15,000 strong Lechitic sub-ethnic group traditionally present in what is now the present-day Warmian-Masurian Voivodeship, Poland. In 2011 Polish census, 1376 individuals declared themselves to be Masurian either as a first or secondary identification. Before World War II and its post-war expulsions, Masurians used to be a more numerous ethnic group found in the southern parts of East Prussia for centuries following the 16th century Protestant Reformation. Today, most of Masurians live in what is now Germany and elsewhere.
They are descended from Masovians (Polish: Mazowszanie; German: Masowier), who were Polish settlers from Mazovia. These settlers moved to the Duchy of Prussia during and after the Protestant Reformation. They spoke Masurian dialect. Since the middle 19th century, High German was increasingly used among Masurians as opposed to Low German used by most of East Prussia's German population. Many Masurians were often bilingual in German and Polish languages. In the 19th century, the Masuria region of East Prussia was named after the Masurians.