The Kingdom of Prussia briefly held land in Estonia.

The story behind the answer

False. Estonia was never part of the Kingdom of Prussia (1701–1918). Its rulers shifted from Denmark (1219–1346) to the Livonian Order (a branch of the Teutonic Knights), then to Sweden (1561–1721), and finally to the Russian Empire after the Great Northern War (Treaty of Nystad, 1721).

The mix-up often comes from conflating German crusader states in the Baltic with Prussia. While the Teutonic and Livonian Orders were Germanic and active nearby, the later Kingdom of Prussia was centered in Brandenburg and East Prussia and never extended to Estonia. Memory tip: Estonia’s path is “Danes → Knights → Swedes → Russians”—no Prussians.