Rondônia is one of the 26 states of Brazil, located in the northern subdivision of the country. It is bordered by Acre in the west, Amazonas in the north, Mato Grosso in the east, and Bolivia in the south. Rondônia has a population of 1,815,000 as of 2021. It is the fifth least populated state. Its capital and largest city is Porto Velho, bathed by the Madeira River. The state was named after Cândido Rondon, who explored the north of the country during the 1910s. The state, which is home to c. 0.7% of the Brazilian population, is responsible for c. 0.3% of the Brazilian GDP.