The U.S. Census Bureau is the primary resource for U.S. demographic data (United States, Puerto Rico and the Island Areas). The Census Data Portal fairly easy to use, and convenient since it includes data from several censuses and surveys including:
Stats America gives you one-stop access to many useful U.S. data sites and tools especially useful for economic development. Some of the things included on the site are:
StatsAmerica is a service of the Indiana Business Research Center at Indiana University's Kelley School of Business. This initiative is funded in part by the U.S. Commerce Department's Economic Development Administration.
The portal into the Census Bureau's Economic Statistics programs and surveys.
The Economic Census is the official five year census of American business, and helps set the Gross Domestic Product (GDP) and Producer Price Index (PPI).
https://www.census.gov/mso/www/training/pdf/econ_Dec2012.pdf