| San Justo | |
| Native Name Lang: | es |
| Settlement Type: | City |
| Pushpin Map: | Argentina |
| Pushpin Map Caption: | Location of San Justo in Argentina |
| Coordinates: | -30.7833°N -95°W |
| Subdivision Type: | Country |
| Subdivision Name: |  Argentina |
| Subdivision Type1: | Province |
| Subdivision Type2: | Department |
| Subdivision Name2: | San Justo |
| Leader Party: | Socialist Party |
| Leader Title: | Mayor |
| Leader Name: | Mario Ruben Silvestrini |
| Unit Pref: | Metric |
| Area Total Km2: | 790 |
| Population Total: | 21624 |
| Population As Of: | 2010 |
| Population Density Km2: | auto |
| Timezone1: | ART |
| Utc Offset1: | -3 |
| Postal Code Type: | CPA base |
| Postal Code: | S3040 |
| Area Code Type: | Dialing code |
| Area Code: | +54 3498 |
San Justo is a city in the center region of the province of Santa Fe, Argentina, 99 km north from the provincial capital. It had about 22,000 inhabitants at the and it is the head town of the San Justo Department.
Founded in 1868 by Mariano Cabal, San Justo attained the status of a comuna (commune) on 13 July 1887 and the following year the Ferrocarril Provincial de Santa Fe arrived on 1 September 1888. It became a city on 17 September 1959. On January 10, 1973, the town was struck by a destructive tornado.