What is the smallest geographic unit available for analysis?

Public use files do not include geographic regions. In the Data Analysis System (DAS), variables for state and census region are available in the multi-year restricted-use files. Substate region, county, and metropolitan area are available in the 10-year combined restricted-use files. 

If a user applies for access to the data in the Research Data Center (RDC), the smallest geographic unit available for analysis is the Census block. However, final tables for publication may not contain information on geographic areas with a population smaller than 100,000 people.