The province neighbours Bulgaria to the north along a 180-kilometre (110 mi) long border.

[1] The province's and its central city's name means "the land of the forties" in Turkish and it may refer either to the forty Ottoman ghazis sent by the sultan Murad I to conquer the city for the Ottoman Empire in the 14th century or to the forty churches reported to be situated in the region before the Ottoman conquest, as attested by the former name of Kırklareli (Kırk Kilise in Turkish; Σαράντα Εκκλησιές).

The districts to the south and west are more populated because the land is better suited for agriculture and industrial development.

[3] It was governed by an Inspector General, who had extensive authorities over civilian, military and educational matters.

A syrup called "Hardaliye", made of grape, cherry leaves and mustard seeds, is a non-alcoholic beverage special to the region.