"Data USA puts public US Government data in your hands. Instead of searching through multiple data sources that are often incomplete and difficult to access, you can simply point to Data USA to answer your questions"

This is about the Census API

"As the amount of data available to us expands at a dizzying pace, the demand for reliable, timely and objective analysis of the data is growing even faster. Our researchers produce papers, speak at conferences and contribute to their fields of expertise on subjects as varied as our economy and society: health, crime, income, education, housing conditions, productivity, innovation, entrepreneurship, and more. Underpinning our data products is research on the statistical methods we use to collect it.U.S. Census Bureau "Working Papers" have not undergone the review and editorial process generally accorded official Census Bureau publications. These working papers are intended to make results of Census Bureau research available to others and to encourage discussion on a variety of topics."

"Explore hundreds of measures of child wellbeing and policy analysis from a unique information source that documents diversity, opportunity, and equity among US children" From The Institute for Child, Youth and Family Policy (ICYFP) at Brandeis University’s Heller School for Social Policy and Management.

"IPUMS-USA is a project dedicated to collecting and distributing United States census data. Its goals are to:
Collect and preserve data and documentation; Harmonize data; Disseminate the data absolutely free!"

"The National Historical Geographic Information System (NHGIS) provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2011."