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

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

The department has about 95,000 inhabitants, which are distributed in 37 districts (mostly small municipalities and communes).

Other cities and towns are Colonia Cavour, Colonia San José, Cululú, Elisa, Empalme San Carlos, Felicia, Franck, Grutly, Hipatia, Humboldt, Ituzaingó, Jacinto L. Arauz, La Pelada, Las Tunas, María Luisa, Matilde, Nuevo Torino, Pilar, Progreso, Providencia, Pujato Norte, Rivadavia, Sa Pereira, San Agustín, San Carlos Centro, San Carlos Norte, San Carlos Sud, San Jerónimo del Sauce, San Jerónimo Norte, San Mariano, Santa Clara de Buena Vista, Santa María Centro, Santa María Norte, Santo Domingo, Sarmiento, and Soutomayor.

The name of this department (which means "The Colonies") derives from the fact that it was settled mostly by immigrant families under the system of agricultural colonies, of which Esperanza was the first formally organized in Argentina.