Mrągowo [mrɔŋˈɡɔvɔ] (until 1947 Polish: Ządźbork [ˈʐɔɲd͡ʑbɔrk]; German: Sensburgⓘ; Masurian: Zondzbork) is a resort town in the Warmian-Masurian Voivodeship of northeastern Poland, with 21,889 inhabitants (2019).

The town is located in the historical region of Masuria, within the Masurian Lake District, about 60 km (37 mi) east of Olsztyn.

[4] The Polish secret resistance was active and smuggled weapons through the town to the Russian Partition of Poland during the January Uprising.

[5] In August 1863, the Prussians discovered the activity, carried out arrests of local resistance members and seized a shipment of weapons headed to the town.

[7] Following World War I, as a condition of the Treaty of Versailles, the League of Nations held the East Prussian plebiscite on 11 July 1920 to determine if the people in the southern districts of East Prussia wanted to remain within the Free State of Prussia and Germany or to join the Second Polish Republic.

Before the vote German nationalists engaged in brutal excesses, which remained unhindered by meagre presence of Allied forces; a Scottish regiment only once visited the city, and only to demonstrate a music orchestra.

[9] 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.