Schwarzburg is a municipality in the valley of the Schwarza (German: Schwarzatal) in the district Saalfeld-Rudolstadt in Thuringia, Germany.
First mentioned in 1071 as Swartzinburg. The (now-ruined) castle was from the 12th century the seat of the Counts of Schwarzburg. Then Rudolstadt became seat of the new line of Schwarzburg-Rudolstadt.
On August 11, 1919, while on holiday in Schwarzburg, Friedrich Ebert — the first Reichspräsident of Germany — signed the Weimar constitution, the first democratic constitution of Germany.