Giornico is a municipality in the district of Leventina in the canton of Ticino in Switzerland .

Giornico is first mentioned around 935-94 as de Iudicibus Giornicensis. In 1202 it was mentioned as Iornico, and around 1210-58 it was mentioned as Zurnigo. Formerly, it was known by the German names of Yrnis or Girnis.

In the Battle of Giornico on 28 December 1478 a Swiss force of 600 defeated 10,000 Milanese troops.

Giornico has an area, as of 1997, of 19.48 square kilometers (7.52 sq mi).