Allendorf is a municipality in the Saalfeld-Rudolstadt district in Thuringia.

The village was first mentioned in documents in 1196-1210 or 1221.

Not far north of the village is the Holy Mountain. North of the summit is the Bear Cave, where bones of deer, wild horses and wild cats have been found. Until 1918, the village belonged to the overlordship of the Principality of Schwarzburg-Rudolstadt.

There was a manor with 100 hectares of farmland in the village, which was leased by Walter Oertel in 1923. After the Second World War, the farm was subject to the development of agriculture in the GDR.

Allendorf has been part of the Mittleres Schwarzatal administrative community since 1993. After its dissolution on January 1, 2019, Königsee became the fulfilling municipality for Allendorf.