Hörnumⓘ (Sölring Frisian: Hörnem, Danish: Hørnum) is a municipality in the district of Nordfriesland, in Schleswig-Holstein, Germany.

The southern tip of the island remained unsettled though for a long time, because not only storm surges but also shifting dunes, which would repeatedly bury houses, made a colonisation difficult.

Only after a wooden wharf had been constructed, a regular ship line to Hamburg via Cuxhaven took up operations on 29 June 1901.

The core of today's Hörnum is the Weiße Siedlung (White Housing Estate) around Strandstraße, Hafenstraße and Blankes Tälchen, built by the military starting in 1920.

In both World Wars, Hörnum was deemed a strategically important location which needed special defense.

At the beginning of World War I, island guards were stationed on Amrum, Sylt and Rømø (today in Denmark), who used light signals to communicate.

From the List "Elbow" peninsula in the north to Hörnum in the south, bunkers and shelters were dug into the dunes of Sylt and wired with telephone lines.

Mostly elderly, local soldiers were tasked with searching the horizon for hostile troops, but the island did not witness any combat.

The outbreak of war prevented the project from being finished and so the gaps in the colony, which was designed as a garden city, have since been filled with post-war buildings.

The number of inhabitants in Hörnum exploded due to the opening of the naval air station and the adjacent quarters and rose above 1,000 when the troops brought their families to the island.

In 1947, the village briefly provided shelter for more than 2,000 refugees from Germany's former eastern territories and also 40 families from Heligoland dwelt there after the evacuation of their island (occupied by the United Kingdom).

When St. Thomas' church was built in 1970, the St. Martin building shortly served as a kindergarten and a storage for Strandkorb beach chairs.

Since 1974, this so-called Norwegian House is seat of the Wadden Sea Conservation Station (Schutzstation Wattenmeer), an environmental protection society, and since 1989 also serves as a youth club.

The Hörnum Yacht Club was created and a new ticket vending facility for Adler shippings was opened.

Hörnum's original function as a military town has been completely replaced by tourism as the main means of income.

The Schutzstation Wattenmeer offers information on the Wadden Sea and the salt marshes and promotes the protection of the local landscape among tourists.

Another attraction is hiking around the Hörnum-Odde, the island's southernmost edge, which due to erosion is constantly shrinking.