It is not generally known that two Lithuanian counties - Tauroggen (Lithuanian, Taurage; Polish, Taurogi) and Serrey (Lithuanian, Seiriai/Serijai; Polish, Sereje) - were a part of the Kingdom of Prussia for a little over a century from 1691 to 1793 (excluding a brief Swedish occupation from 1702-1709), with Tauroggen a northern extension of the East Prussian Memelland and Serrey a separated territory to the east.

Tauroggen, the residence of the Radziwiłł family since 1655, came into the possession of Brandenburg-Prussia as a result of the marriage of the Margrave Ludwig of Brandenburg (son of Friedrich Wilhelm) with Princess Ludwika Karolina Radziwiłł, who was born in Königsberg (capital of East Prussia/Ostpreußen) and died in Brieg, Silesia (Schlesien). She was a devout Calvinist. As a result, the city of Tauroggen became a centre of Lutheranism in Lithuania, an otherwise Catholic country.

Tauroggen was turned over to Poland in 1793 in compensation for the return of Danzig, and annexation of South Prussia (Südpreußen/Posen), to Prussia before passing to the Russian Empire following the final partition of Poland. It was incorporated into the Republic of Lithuania in 1920 following the First World War. There is almost no information available on Serrey.

It is unlikely that Tauroggen ever had a substantial German population in spite of a century of Prussian rule and that it retained its essentially Lithuanian character. There must have been a German presence if not solely because of its close proximity to East Prussia-proper though I have been unable to find any information on this. Serrey was much farther away from Prussia, lying east of Sudauen (Suwałki/Svalkai) in Polish Lithuanian territory and probably had little in the way of German influence.