U.S. Census Statistics: Census & ACS: Datasets

Aggregate U.S. census information from 1790-2000 in machine-readable format. Historical boundary files in shapefile format. Free registration required.

1850-present.
Create or download extracts of U.S. census microdata. Some online analysis also available.

"The Inter-university Consortium for Political and Social Research (ICPSR), established in 1962, is an integral part of the infrastructure of social science research. ICPSR maintains and provides access to a vast archive of social science data for research and instruction." Search this site for holdings. Data downloads are free of charge from MSU registered computers.

An ACS Summary File is a set of comma-delimited text files that contain all of the Detailed Tables for the ACS 1-year, 3-year or 5-year estimates. For example, the 2008 ACS 1-year Summary File includes hundreds of comma-delimited text files that are best viewed in a spreadsheet or using statistical software.