After World War I, the southern half of Sankt Wendel had to be ceded to the newly created Saar Territory, and the small part remaining in Prussia was then officially called the Restkreis Sankt Wendel ("remaining district of Sankt Wendel"). In 1937 the Oldenburgian District of Birkenfeld was merged with the remaining Sankt Wendel District to form the new Prussian District of Birkenfeld.
Following World War II, on 18 July 1946 by the French Ordinance No. 8, twenty-four more villages were ceded to the new Délégation Supérieure de la Sarre, which became the new Saar Protectorate in 1947. Not until 1970 were the present borders of the district set.