The decision was handed over to the League of Nations, which confirmed the border, and Poland received roughly one third of the plebiscite zone by area, including the greater part of the industrial region.

Polish immigration from Galicia, Congress Poland and Prussian provinces into Upper Silesia during the 19th century was a major factor in their increasing numbers.

[7] Polish authors before 1918 estimated the number of Poles in Prussian Upper Silesia as slightly higher than according to official German censuses.

[8] The three western districts of Falkenberg (Niemodlin), Grottkau (Grodków) and Neisse (Nysa), though part of Regierungsbezirk Oppeln, were not included in the plebiscite area, as they were almost entirely populated by Germans.

[13] A feature of the plebiscite campaign was the growing prominence of a strong autonomist movement, the most visible branch of which was the Bund der Oberschlesier/Związek Górnoślązaków, an organisation attempted to gain promises of autonomy from both states and possible future independence for Upper Silesia.

However, the districts of Pless (Pszczyna) and Rybnik in the southeast, as well as Tarnowitz (Tarnowskie Góry) in the east and Tost-Gleiwitz (Gliwice) in the interior showed considerable Polish majorities, while in Lublinitz (Lubliniec) and Groß Strehlitz (Strzelce Opolskie) the votes cast on either side were practically equal.

In late April 1921, when pro-Polish forces began to fear that the region would be partitioned according to the British plan, elements on the Polish side announced a popular uprising.

German-speaking spokesmen and German officials complained that the French units of the Upper Silesian army of occupation supported the insurrection by refusing to put down violent activities or to restore order.

Simultaneously with those events, the Interallied Commission pronounced a general amnesty for the illegal actions committed during the recent violence except for acts of revenge and cruelty.

Agreements between the Germans and Poles in Upper Silesia and appeals issued by both sides, as well as the dispatch of six battalions of Allied troops and the disbandment of the local guards, contributed markedly to the pacification of the district.

According to Article 88 of the Treaty of Versailles all inhabitants of the plebiscite district older than 20 years of age and those who had "been expelled by the German authorities and have not retained their domicile there" were entitled to return to vote.

[41] There were cases of votes being cast in the name of already deceased persons who died outside of Upper Silesia, and since their deaths were registered" in comparatively inaccessible German registration departments in Central Germany", it was often difficult to detect voter fraud.

[41] The Polish population of Silesia overwhelmingly consisted of poor workers and small farmers, who owned no real property and were highly dependent on the German authorities to provide appropriate instrastructure.

All offices and industries were controlled by the German population, who exerted an overwhelming pressure on Poles to vote for Germany, and they "frequently exceeded their lawful powers and supported many forms of anti-Polish activities".

[41] Emil Julius Gumbel investigated and condemned the cases of widespread intimidation and murders by Freikorps and Selbstschutz divisions and remarked that “a denunciation, a suspicion without foundation under the given circumstances, was sufficient.

Machray concludes that given the aggressive anti-Polish campaign conducted by local authorities and German volunteers, "the results were far from being an objective reflection of the true desires of the oppressed people".

[17] In total, over 700 towns and villages voted to secede from Germany and become part of Poland, especially in the rural districts of Pszczyna,[33] Rybnik,[36] Tarnowskie Góry,[37] Toszek-Gliwice,[22] Strzelce Opolskie,[23] Bytom,[20] Katowice,[25] Lubliniec,[29] Zabrze,[24] Racibórz,[34] Olesno,[35] Koźle[21] and Opole.