After the First World War, Tønder was detached from Germany in spite of the majority of its population casting a pro-German vote in the Schleswig Plebiscites - as Tønder was included in Zone I, which as a whole had a strong pro-Danish majority.A wartime aircraft hangar survives, as do some of the ancillary buildings, but only the foundations remain of the large airship hangars.
Seven Sopwith Camels from the aircraft carrier HMS Furious bombed the base, hitting two of the three airship hangars.
In the 1920s, when the Schleswig Plebiscite incorporated Northern Schleswig into Denmark, 76.5% of Tønder's inhabitants voted to remain part of Germany and 23.5% voted to join Denmark.
During World War I, a Zeppelin base was operated in Tønder by the Imperial German Navy.
The Zeppelins L.54 and L.60 inside one hangar were destroyed and a balloon inside the other was damaged.
After this, Tønder was abandoned as an active airship base, and was used only as an emergency landing site.
In 1532 it was hit by severe floods, with water levels reaching 1.8 m in St Laurent's church, 5.3 m above sea level.
In the 1550s, Tønder's port lost direct access to the sea due to dykes being built to the west of town at the direction of Duke Hans the Elder of Schleswig-Holstein-Haderslev, the son of Frederick I of Denmark.
The first mention of Tønder might have been in the mid-12th century, when the Arab geographer Muhammad al-Idrisi mentioned the landmark Tu(r)ndira, which might have been a reference to either Tønder, or the nearby town of Møgeltønder.
Tønder was granted port privileges by the Hanseatic League in 1243, making it Denmark's oldest privileged market town.
The town center is dominated by houses from the late 17th and early 18th century, when the town experienced rapid growth as a result of its lace industry.
Prior to 1864, Tønder was situated in the Duchy of Schleswig, so its history is intertwined with the contentious history of Schleswig-Holstein.