The poverty rate was 15% in 2011, meaning 46.2 million Americans were in poverty, staying flat after three previous years of increases.
Real median income of households in the country dropped by 1.5%.
The average poverty threshold for a family of four in 2011 was $23,021 (Â£14,300).
Income inequality, as measured by the Gini index, increased by 1.6% in 2011, the first time there has been an annual rise in the index since 1993.
The percentage of Americans lacking health insurance fell to 15.7% from 16.3%, the report also said.
Poverty in the US reached a record high in 2010, at 15.1%.
The percentage of Americans living in poverty is statistically unchanged from 2010's record high, even as household income fell, a US Census report says.