San Quirico d'Orcia is a comune (municipality) in the Province of Siena in the Italian region Tuscany, located about 80 km southeast of Florence and about 35 km southeast of Siena inside the Valdorcia landscape. As of 31 December 2004, it had a population of 2,526 and an area of 42.2 km2.
The municipality of San Quirico d'Orcia contains the frazioni (subdivisions, mainly villages and hamlets) Bagno Vignoni and Vignoni.
San Quirico d'Orcia borders the following municipalities: Castiglione d'Orcia, Montalcino, Pienza, San Giovanni d'Asso.