The Province of Sondrio (provincia di Sondrio) is in the Lombardy region of northern Italy. Its provincial capital is the city of Sondrio. As of 2017, it has a population of 181,403.
The Province was established in 1815, within the Kingdom of Lombardy–Venetia, combining the valleys of Valtellina, Valchiavenna and Bormio.
Before the Roman conquest, the territory was inhabited by Celts (Lepontii) and Rhaetians (Camunni). The Romans included this area in their Cisalpine Gaul province.
After the fall of the Western Roman Empire, it came under the control of the Lombards and was first ruled by feudal lords from the local area. During the Middle Ages it belonged to the Kingdom of Italy. In the 14th century it fell under the rule of the Duchy of Milan due to the House of Visconti and House of Sforza. Sondrio and Valtellina were strategically important in the politics of Europe, especially in the sixteenth and 17th century religious wars, due to their connections to Europe by Sondrio's Spluga Pass and valleys. Upon the collapse of the Duchy of Milan, rule over Sondrio was exercised by the Swiss Canton of Graubünden. Valtellina was invaded in 1622 by the Spanish Governor of Milan as the valleys had been used to transport troops around Europe; the Spanish efforts were assisted by a 1620 revolt in Valtellina against the Swiss.
The Peace of Westphalia (1648) secured peace in the region and granted the region to the Canton of Graubünden. In 1797, the Republic of Valtellina was formed but was quickly conquered by the French to become a component of the Cisalpine Republic client state. The Congress of Vienna (1815) Sondrio and Valtellina as a province of the Austrian Kingdom of Lombardy–Venetia.
As most of Lombardy region was absorbed into Kingdom of Sardinia in 1860, Sondrio and Valtellina were also absorbed into Sardinia.
The Province of Sondrio is a mostly mountainous, sparsely populated area in the north of Lombardy. It borders on the Swiss canton of Graubünden to the north, the Provinces of Como and Lecco to the west, the Province of Bergamo to the south and the Provinces of Brescia, Trento and Bolzano to the east.