Oldsum was first recorded in 1462 as
Uluersum. During the 17th and 18th centuries, Oldsum, Klintum and Toftum were important
whaling villages. A census in 1787 showed that a total of 211 of the inhabitants of the three places were seafarers. One of the most successful whalers,
Matthias Petersen (1632–1706) lived in Oldsum proper. In his lifetime he was able to catch 373 whales, his tomb can still be visited in the graveyard of the St. Laurentii church in Süderende. As a part of Westerland Föhr, Oldsum belonged to the Royal Enclaves of
Denmark and thus was a direct part of the Danish crown while Osterland Föhr belonged to the
Duchy of Schleswig. Only when Denmark lost Schleswig to
Prussia in the
Second Schleswig War, Oldsum became a part of Schleswig-Holstein. ==Politics==