A plebiscite, under the
Treaty of Versailles, was held on 11 July 1920 to determine whether the people of the district of Allenstein wished to remain in East Prussia or
become part of Poland. Special postage stamps were produced by overprinting German stamps; these were on sale from 3 April 1920.
14 values, ranging from 5pf to 3m were overprinted in two different overprints one which read PLÉBISCITE / OLSZTYN / ALLENSTEIN and the other
read TRAITÉ / DE / VERSAILLES / ART. 94 et 95 inside an oval whose border gave the full name of the plebiscite commission.
Postal Stationery - postcards and letter cards were also produced with the two different overprints.
Under the Treaty of Versailles, Allenstein was placed under the authority of the Inter-Allied Commission.
British and Italian troops began arriving on 12 February 1920 to supervise the plebiscite.
The plebiscite, which was held on 11 July 1920, produced 362,209 votes (97.8%) for East Prussia and 7,980 votes (2.2%) for Poland.
The formal handover from the Inter-Allied Commission to German authorities occurred on 16 August 1920.
The international use of these stamps and stationery was discontinued on 20 August 1920; but they continued to be valid for internal use till the end of October 1920.
On 2 August 1945 the city was placed under Polish administration in accordance with the Potsdam Agreement and renamed to Olsztyn.