The Fort de Plainbois is a twentieth-century Swiss fortification located at the east end of the Jura Mountains near the Swiss border with France.

Deactivated as a military post in the 1990s, it has been offered for sale by the Swiss Defense Forces.

The Fort de Plainbois is located to the east of Delémont It is part of the Border Line defenses built by Switzerland in the late 1930s, prior to a shift in Swiss priorities to the National Redoubt in the Alps.

Two artillery casemates containing 75mm guns comprised the fort's main armament.

The commune of Bourrignon was interested in buying the fort to preserve it: however, competing bidders proposed to use the site as a center for natural therapy.