Landgrave occasionally continued in use as the subsidiary title of such nobility as the Grand Duke of Saxe-Weimar, who functioned as the Landgrave of Thuringia in the first decade of the 20th century, but the title fell into disuse after World War I.
The jurisdiction of a landgrave was a landgraviate and the wife of a landgrave was a landgravine. Examples: Landgrave of Thuringia, Landgrave of Hesse, Princely (Gefürsteter) Landgrave of Leuchtenberg (around a Bavarian castle; later made a duchy).
Landgraviate refers to the rank, office, or territory held by a landgrave.
Landgravine (German: Landgräfin) refers to the wife of a Landgrave or one who exercises the office or holds the rank in her own right.
Source:
http://en.wikipedia.org/wiki/Landgrave