The state of Rio de Janeiro is located within the Brazilian geopolitical region classified as the Southeast (assigned by IBGE). Rio de Janeiro shares borders with all the other states in the same Southeast macroregion: Minas Gerais (N and NW), Espírito Santo (NE) and São Paulo (SW). It is bounded on the east and south by the Atlantic Ocean. Rio de Janeiro has an area of 43,653 km². Its capital is the city of Rio de Janeiro, which was the capital of the Portuguese Colony of Brazil from 1763 to 1815, capital of the United Kingdom of Portugal, Brazil and the Algarves from 1815 to 1822, and capital of independent Brazil from 1822 to 1960.
The state's largest cities are Rio de Janeiro, São Gonçalo, Duque de Caxias, Nova Iguaçu, Belford Roxo, Niterói, São João de Meriti, Campos dos Goytacazes, Petrópolis, Volta Redonda, Magé, Itaboraí, Macaé, Mesquita, Cabo Frio, Nova Friburgo, Angra dos Reis and Barra Mansa.
Rio de Janeiro is the smallest state in the Southeast macroregion and one of the smallest in Brazil. It is, however, the third most populous Brazilian state—with a population of 16 million of people in 2011 (making it the largest population density state in Brazil)—, and the third longest coastline in the country (after those of the states of Bahia and Maranhão).