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.
Both first-time and seasoned users can benefit from the Using the NHGIS Data Finder guide and other tutorial documents that are available.
If you have a question, there is a good chance you will find the answer here.
NHGIS offers a wide range of content, covering 220 years, varying geographic levels, and a range of demographic, social, agricultural, economic and housing-related topics. This page provides a summary of what is available.
NHGIS provides shapefiles that can be opened in nearly all GIS software packages. This includes Esri ArcGIS along with many other for-purchase and open source software. An alternative to using a GIS is Social Explorer, a website that enables basic online mapping and analysis of a large portion of NHGIS content.