The department was created on June 16, 1837, with part of Cerro Largo and Maldonado departments. It was first named as Minas. In March 1888, it was asked that theChamber of Deputies raised thesettlement hierarchy of the village of Minas to be a town and to change the department's name to Lavalleja. The first was approved. From then, and until December 26, 1927, when the name was changed to Lavalleja, widespread debates about the matter were held. There was political will to designate a department under the name of the head of theLiberation Crusade, but not at the expense of Minas, even considering creating a new department named Lavalleja, being rejected afterwards.
Most of the north border of the department is formed by theOlimar Chico River andOlimar Grande River. Most of the middle and north part of the department is crossed by many streams, flowing from northwest and south directions towards the northeast of the department, all being tributaries of Río Cebollati, which flows to the northeast and discharges intoLake Merín, a natural border withBrazil. These streams, from north to south, are: Arroyo Gutiérrez, Arroyo de los Molles, Arroyo de los Chanchos, Arroyo Polanco, Arroyo Barriga Negra, Arroyo Tapes Grande, Arroyo Marmarajá and finally Arroyo Aiguá, which forms most of the east border of the department. In the south of the department, flowing from east to west isSanta Lucía River with its tributaries, Arroyo del Soldato, Arroyo Campanero Grande and Arroyo Verdún. Another stream in the south is Arroyo Solís Grande, which forms part of the natural border withCanelones Department and flows south discharging into theRío de la Plata nearGregorio Aznárez.
The south part of theCuchilla Grande hillrange crosses the department from the south to northwest. In the south and near Minas, there are two important tourist attractions, the hills ofCerro Arequita andCerro Verdún (which is also a pilgrimage sanctuary). A bit further to the north is the hill Cerro Espuelitas.
The railroad track Montevideo-Minas is active only for cargo trains of the Línea Minas. 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.
