From the Wikipedia page 
The Territoire de Belfort (French pronunciation: [tɛʁitwaʁ də bɛlfɔʁ]) is a department in the Bourgogne-Franche-Comté region of eastern France.
Its departmental code is 90, and its prefecture (capital) is Belfort. There is a single arrondissement (Belfort), which is subdivided into 9 cantons and thence into 102 communes.
The administrative district Territoire de Belfort was created under the terms of the 1871 Treaty of Frankfurt. The German Empire annexed almost all of Alsace, but the French were able to negotiate retention of the Territoire de Belfort which thereby was separated from the rest of Alsace (where it had been part of the department of Haut-Rhin).