It is located in the southeast of the country, bordered to the north by the department of Treinta y Tres to the east with Rocha, to the south with Canelones and Maldonado, and to the west to Florida.

The department is named in honor of Brigadier Juan Antonio Lavalleja, who had distinguished military and political action in the country's independence.

In March 1888, it was asked that the Chamber of Deputies raised the settlement hierarchy of the village of Minas to be a town and to change the department's name to Lavalleja.

Route 14, which crosses the country in a west-to-east direction, passes through the north of the department, joining it with Mercedes, Trinidad and Durazno to the west and the Atlantic coast to the east.

Another track, following the path of Route 14 through the department, is active for cargo trains from Montevideo of the Línea Río Branco, which continues into Brazil.