Treaty of Dappes
1862 CE.
Shown on the map at 46.434°, 6.077°.
The Treaty of Dappes was concluded on 8 December 1862 between France and the Swiss Confederation. Resolving a long-standing border dispute between the two countries, the accord awarded the Vallée des Dappes (which had been controlled by Switzerland since 1815) to France, in exchange for a comparable piece of territory just to the north. The treaty is noteworthy for dividing the tiny village of La Cure between the two countries, with the new border bisecting not just the town itself, but several structures within it.
Text from the Wikipedia article Treaty of Dappes, licensed CC BY-SA 4.0.