"Roger Lustig" wrote
Technically, there weren't any regions that were Poland in 1871-81,"Grossherzogtum Posen" was rather a short lived entity. Following its
establishment in 1815 (Vienna Congress) it ceased to exist in 1849. This was
an autonomous entity of Prussia, formed to satisfy Polish national
aspiration. Following uprisings in 1846 and 1848, Prussian administration
has changed its name to Provinz Posen.
BTW, Polish speakers were also numerous in the other parts of Prussia: Upper
Silesia, East Prussia and Pomerania.