The San Justo Department (in Spanish, Departamento San Justo) is an administrative subdivision (departamento) of the province of Santa Fe, Argentina.

Starting from the north and going clockwise, it limits with the departments of Vera, San Javier, Garay, La Capital, Las Colonias, and San Cristóbal.

San Justo is thus one of only three provincial departments that do not share a border with another province.

The head town is San Justo (population 22,000).

The others are Angeloni, Cayastacito, Colonia Dolores, Colonia Esther, Gobernador Crespo, La Camila, La Criolla, La Penca y Caraguatá, Marcelino Escalada, Naré, Pedro Gómez Cello, Ramayón, San Bernardo, San Martín Norte, Silva, Vera y Pintado, and Videla.