The 2009 Thuringian state election was held on 30 August 2009 to elect the members of the 5th Landtag of Thuringia. It was held on the same day as the 2009 Saarland state election and the 2009 Saxony state election. The incumbent Christian Democratic Union (CDU) government led by Minister-President Dieter Althaus was defeated. The CDU subsequently formed a grand coalition with the Social Democratic Party (SPD). Althaus resigned after the election due to his party's poor performance, which was far below expectations. He was succeeded by fellow CDU member Christine Lieberknecht, who was elected as the new Minister-President.

The Landtag of Thuringia is the parliament of the German federal state of Thuringia. It convenes in Erfurt and currently consists of 90 members from seven parties. According to the free state's constitution, the primary functions of the Landtag are to pass laws, elect the Minister-President and control the government of Thuringia.