On February 12, 1821, by mandate of the so-called Reglamento Provisional, the Department of Tarma was created in Huaura, integrated on the basis of the Intendancy of Tarma, a territorial district of the viceroyalty of Peru.

The new department was only made up of the provinces of Tarma and Jauja since the northern provinces of the old intendancies (Conchucos, Huaylas, Huamalíes, Huánuco and Cajatambo) were grouped in the Department of Huaylas.

The political foundation of this demarcation was carried out by José de San Martín.

In effect, after two years and nine months, the dictator Simón Bolívar by Decree Law of September 13, 1825 ordered the separation of the provinces of Huaylas, Conchucos and Cajatambo (with which he created the department of Huaylas again) and would change the name the department, baptizing it as the "Department of Junín", as a tribute to the battle won against the royalist army in these areas that belonged at that time to the constituency of Tarma.

Later, the wealth of Cerro de Pasco influenced this city to prevail as the head of the department.