Urban informal settlements are often under-recognized in national and regional surveys. A lack of quality intra-urban data frequently contributes to a one-size-fits-all public health intervention and clinical strategies that rarely address the variegated socioeconomic disparities across and within different informal settlements in a city. The 2010 Brazilian census gathered detailed population and place-based data across the country's informal settlements. Here, we examined key socio-demographic and infrastructure characteristics that are associated with health outcomes in Rio de Janeiro with the census tract as the unit of analysis. Many of the city's residents (1.39 million people, 22 % of the population) live in informal settlements. Residents of census tracts in Rio de Janeiro's urban informal areas are younger, (median age of 26 versus 35 years in formal settlements), and have less access to adequate water (96 versus 99 % of informal households), sanitation (86 versus 96 %), and electricity (67 versus 92 %). Average per household income in informal settlement census tracts is less than one third that of non-informal tracts (US\$708 versus US\$2362). Even among informal settlements in different planning areas in the same city, there is marked variation in these characteristics. Public health interventions, clinical management, and urban planning policies aiming to improve the living conditions of the people residing in informal settlements, including government strategies currently underway, must consider the differences that exist between and within informal settlements that shape place-based physical and social determinants of health.