Encyclopedia Britannica 1842, gives 1825 data for West Prussia and Posen:
https://play.google.com/books/reader?id=fVhBAAAAcAAJ&hl=en_GB&pg=GBS.PP1
Georg Hassel has a lot of data about ethnic structure in his book from 1823:
Provinz (Grand Duchy) Posen: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA43
West Prussia, Georg Hassel: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA42
West Prussia, Karl Andree*: https://books.google.pl/books?id=xgUEAAAAYAAJ&pg=P212
Pommern: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA31
Oppeln Silesia: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA34
Breslau Silesia: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA33
^^^
Other authors give similar numbers of Poles in Breslau Silesia (Kamusella, Ladenberger and Michałkiewicz for year 1840 give 80,000 Poles in Breslau Regency and 566,000 in Oppeln Regency; S. Plater gives 600,000 Poles in all of Silesia in 1824).
Liegnitz Silesia: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA34
Brandenburg: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA30
^^^
But according to T. Kamusella, in year 1815 there were still 200,000 Sorbian-speakers in Brandenburg (and 50,000 in Saxony):
In the link below August von Haxthausen in his 1839 book has data on East Prussia, by county:
https://books.google.pl/books?id=Gsj1FBg0gvUC&pg=RA1-PA78
County Allenstein (Olsztyn) for example:
Karl Andree* gives for East Prussia 480,000 Poles and Lithuanians (total population 1,080,000):
https://books.google.pl/books?id=xgUEAAAAYAAJ&pg=P218
*Karl Andree, "Polen: in geographischer, geschichtlicher und culturhistorischer Hinsicht", 1831.
Georg Hassel for some reason added East Prussian Poles to East Prussian Lithuanians. However, he also reported 20,000 Curonians and Latvians as well as 2,400 Jews in East Prussia (Andree's data for East Prussia is for year 1824, Hassel's data for year 1819).
Religious structure by Regierungsbezirk, in year 1817:
Ethnically German, Polish and Lithuanian areas in East Prussia:
"Ethnographische Karte von Europa", Heinrich Berghaus, Gotha, 1847:
There is also this book: https://archive.org/details/bub_gb_CqpCAAAAIAAJ
Karl Weinhold, "Die Verbreitung und die Herkunft der Deutschen in Schlesien"
("The Origins and Distribution of Germans in Silesia", published in 1887)
He gives some data on ethnic groups in Silesia in the mid-19th century:
https://play.google.com/books/reader?id=fVhBAAAAcAAJ&hl=en_GB&pg=GBS.PP1
Georg Hassel has a lot of data about ethnic structure in his book from 1823:
Provinz (Grand Duchy) Posen: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA43
West Prussia, Georg Hassel: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA42
West Prussia, Karl Andree*: https://books.google.pl/books?id=xgUEAAAAYAAJ&pg=P212
Pommern: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA31
Oppeln Silesia: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA34
Breslau Silesia: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA33
^^^
Other authors give similar numbers of Poles in Breslau Silesia (Kamusella, Ladenberger and Michałkiewicz for year 1840 give 80,000 Poles in Breslau Regency and 566,000 in Oppeln Regency; S. Plater gives 600,000 Poles in all of Silesia in 1824).
Liegnitz Silesia: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA34
Brandenburg: https://books.google.pl/books?id=31DMAJgQV28C&pg=PA30
^^^
But according to T. Kamusella, in year 1815 there were still 200,000 Sorbian-speakers in Brandenburg (and 50,000 in Saxony):
In the link below August von Haxthausen in his 1839 book has data on East Prussia, by county:
https://books.google.pl/books?id=Gsj1FBg0gvUC&pg=RA1-PA78
County Allenstein (Olsztyn) for example:
Karl Andree* gives for East Prussia 480,000 Poles and Lithuanians (total population 1,080,000):
https://books.google.pl/books?id=xgUEAAAAYAAJ&pg=P218
*Karl Andree, "Polen: in geographischer, geschichtlicher und culturhistorischer Hinsicht", 1831.
Georg Hassel for some reason added East Prussian Poles to East Prussian Lithuanians. However, he also reported 20,000 Curonians and Latvians as well as 2,400 Jews in East Prussia (Andree's data for East Prussia is for year 1824, Hassel's data for year 1819).
Religious structure by Regierungsbezirk, in year 1817:
Ethnically German, Polish and Lithuanian areas in East Prussia:
"Ethnographische Karte von Europa", Heinrich Berghaus, Gotha, 1847:
There is also this book: https://archive.org/details/bub_gb_CqpCAAAAIAAJ
Karl Weinhold, "Die Verbreitung und die Herkunft der Deutschen in Schlesien"
("The Origins and Distribution of Germans in Silesia", published in 1887)
He gives some data on ethnic groups in Silesia in the mid-19th century:
