Ligurian tribes populated the Contea di Nizza prior to its occupation by the Romans. These tribes, conquered by Augustus, had become fully Romanized (according to Theodore Mommsen) by the 4th century, when the barbarian invasions began. In those Roman centuries the area was part of the Regio IX Liguria of Italy.
The Franks conquered the region after the Fall of the Western Roman Empire, and the local Romance populations became integrated within the County of Provence, with a period of independence as a maritime republic (1108–1176). It was initially a semi-autonomous part of the ancient County of Provence, then it became in 1388 a part of the Duchy of Savoy (which became the Kingdom of Sardinia, usually referred to as Piedmont-Sardinia, in 1720).
The region received the name County of Nice during the 15th century, after its integration into the Piedmontese state. From 1388 to 1860 the history of the County of Nice was tied to that of Italian Piedmont-Sardinia. Its historical capital city is Nice.
France annexed the County in 1860, during the Italian Wars of Independence. By an 1858 secret agreement concluded at Plombières between Napoleon III of France and Sardinian prime minister Count Camillo Benso di Cavour, France agreed to support Piedmont in a war against Austria in order to wrest the provinces of Lombardy and Venetia from Austrian rule. In exchange for French military assistance, Piedmont was to cede Nice and Savoy to France. The annexation was temporarily put into doubt after the Italian war of 1859, during which Napoleon III concluded a separate peace with Austria before Venetia could be captured. In March 1860, however, as Piedmont was in the process of annexing Parma, Modena, and the Marches, Napoleon III agreed to sanction Piedmont's Italian acquisitions in exchange for Nice and Savoy. France annexed the provinces by the provisions of the Treaty of Turin, signed on 24 March 1860. There followed plebiscites in Nice on 15 and 16 April and in Savoy on 22 and 23 April, in which the vast majority of the inhabitants of the two territories voted to approve the treaty and join France. France took formal possession of Nice and Savoy on 12 June 1860.