This guide provides pointers on retrieving Census and related demographic statistics via two of the principal databases containing Census data: Social Explorer and Data.census.gov--the Census Bureau's new site for disseminating Census data (separate page still to come). Social Explorer offers more historical data. Explore Census Data offers a greater breadth or recent data. Your choice of one database over another is mainly a matter of personal preference based on ease of use, coverage, and functionality.
The Other resources tab provides additional resources for coverage of Census data.