At the end of World War II the town was overrun by the Red Army during the East Prussian Offensive and lost almost 20% of its buildings. The German population remaining after the evacuation was largely expelled after the war and replaced with Poles. From 1945 to 1947 the city was known by the historic Polish name "Ządzbork". The city's name was changed to the current "Mrągowo" in 1947, in honor of Polish pastor, writer and translator Krzysztof Celestyn Mrongovius (1764–1855), a noted defender of the Polish language in Masuria.