The municipality has the second largest population of the South Fluminense mesoregion, has more than 528 industrial units, a large rail, road and river junction.

It is also close to regional economic centers such as São José dos Campos, Juiz de Fora and Volta Redonda.

The first clue to settlement occurred in 1764 when Francisco Gonçalves de Carvalho obtained with the viceroy D. Antônio Álvares da Cunha a sesmaria to found a farm of cattle and supplies (Fazenda da Posse) between the Paraíba River of the South and the river Bananal, exactly in the place where there was a stream called Barra Seca or Barra Mansa.

In 1764, the Vice King of Brazil, Antônio Álvares da Cunha, granted a sesmaria to the farmer Francisco Gonçalves de Carvalho.

The Barão de Guapi Palace is a historical building of Barra Mansa that received illustrious people like the Princess Isabel.

Over the years, these sesmarias were changed owners, until, around 1827, they arrived, by inheritance, at the hands of Colonel Custódio Ferreira Leite, the Baron of Aiuruoca, founder of the municipality.

Barra Mansa borders 8 municipalities, one of which is in the state of São Paulo According to the Brazilian Institute of Geography and Statistics - IBGE, the population censused in 2022 was 169,899 inhabitants.

The largest steel mill in Latin America, Companhia Siderúrgica Nacional (CSN), is in its conurbation, located in the municipality of Volta Redonda.