| Native Name: | Département de la Sésia |
| Common Name: | Sésia |
| Subdivision: | Department |
| Nation: | the First French Republic and of the First French Empire |
| Year Start: | 1802 |
| Event Start: | Decree of 24 Fructidor, year X[1] |
| Date Start: | 11 September |
| Year End: | 1814 |
| Event End: | Treaty of Fontainebleau |
| Date End: | 11 April |
| P1: | Subalpine Republic |
| Flag P1: | Flag of the Repubblic of Alba.svg |
| S1: | Division of Vercelli |
| Flag S1: | Flag of the Kingdom of Sardinia.svg |
| Image Map Caption: | Administrative map of the Italian portion of the French Empire. |
| Capital: | Vercelli |
| Political Subdiv: | 5 Arrondissements |
| Stat Year1: | 1812 |
| Stat Area1: | 3351.18 |
| Stat Pop1: | 202733 |
Sésia (in French sesja/) was a department of the French Consulate and of the First French Empire in present-day Italy. It was named after the river Sesia. It was formed in 1801, when the Subalpine Republic (formerly the mainland portion of the Kingdom of Sardinia) was intended to be annexed to France. Its capital was Vercelli.
The department was disbanded after the defeat of Napoleon in 1814. At the Congress of Vienna, the Savoyard King of Sardinia was restored in all his previous realms and domains, including Piedmont. Its territory is now divided between the Italian provinces of Vercelli and Biella.
100px|rightThe department was subdivided into the following arrondissements and cantons (situation in 1812):[2]
Its population in 1812 was 202,733, and its area was 335,118 hectares.[2]