Data contained in the ACS Summary File cover demographic, social, economic, and housing subject areas. All Detailed Tables for the ACS 1-year and 5-year estimates are in the Summary File and are listed in Appendix A for their respective data release.
The ACS Summary File covers geographic areas based on "summary levels." A summary level specifies the content and the hierarchical relationships of the geographic elements that are required to tabulate and summarize data. For example, summary level code "040" represents the U.S. states, Washington D.C., and Puerto Rico; while summary level code "050" represents counties and county equivalents within states.
The ACS 1-year estimates are published for areas that have populations above 65,000. The ACS 3-year estimates are no longer published, but historically covered areas with populations above 20,000. The ACS 5-year estimates are published for all geographic areas, including census tracts, block groups, American Indian areas, core based statistical areas, combined statistical areas, Congressional districts, and state legislative districts. View the full list of summary levels published for the Detailed Tables in Appendix B. Data for census block groups are published in American FactFinder, the Census Bureau API, as well as the ACS Summary File. The list of tables in the 5-year Appendix A shows which tables are available at the block group level.
Many resources are available to help users understand the ACS geographic terms and concepts. For additional information, please visit the Geography Reference page at http://www.census.gov/geo/www/reference.html
and the Geography and the ACS page at http://www.census.gov/programs-surveys/acs/geography-acs.html