ICPSR Online. 

ICPSR (Inter-University Consortium for Political and Social Research) maintains a data archive of more than 500,000 files of research in the social sciences. It hosts 16 specialized collections of data in education, aging, criminal justice, substance abuse, terrorism, and other fields

• The Counted The Guardian newspaper's database of Americans killed by police.
• Data.gov
• Data Resource Center for Child & Adolescent Health
• Economic Policy Institute(research, data, and issues of social and economic importance)
• The Gallup Poll (fee for most search results)
• Gallup World Poll
• General Social Survey(personal interview survey of U.S. households)
• Google Dataset Search
• National Council on Public Polls(NCPP)
• Ohio Department of Rehabilitation and Correction
• Pew Research Center
• PollingReport.com
• Public Agenda
• re3data.org - A tool for helping people identify and locate online repositories of research data.
• Substance Abuse and Mental Health Data Archive-Public Use Data Analysis System
• Survey Research Center (Woodrow Wilson School at Princeton University)
• US Census Bureau Poverty
• World Bank data catalog

For ADDITIONAL RESOURCES regarding the census and demographic information on the international, national, state and local level, click here.