| San Martín Department | |
| Native Name Lang: | es |
| Settlement Type: | Department |
| Mapsize: | 180px |
| Pushpin Map Caption: | Location of San Martín in Argentina |
| Coordinates: | -31.75°N -111°W |
| Subdivision Type: | Country |
| Subdivision Name: |  Argentina |
| Subdivision Type1: | Province |
| Subdivision Name1: | Santa Fe |
| Seat Type: | Head town |
| Seat: | Sastre |
| Unit Pref: | Metric |
| Area Total Km2: | 4860 |
| Population Total: | 60698 |
| Population Density Km2: | auto |
| Timezone1: | ART |
| Utc Offset1: | -3 |
The San Martín Department (in Spanish, Departamento San Martín) is an administrative subdivision (departamento) of the province of Santa Fe, Argentina. It is located in the center-south of the province. It limits with the departments of Castellanos (north), Las Colonias (north-east), San Jerónimo (east), and Belgrano (south); the western limit coincides with the interprovincial border between Santa Fe and Córdoba.
The department has over 60,000 inhabitants. Its head town is Sastre. Other towns and cities are Cañada Rosquín, Carlos Pellegrini, Casas, Castelar, Colonia Belgrano, Crispi, El Trébol, Landeta, Las Bandurrias, Las Petacas, Los Cardos, María Susana, Piamonte, San Jorge, San Martín de las Escobas, and Traill.