From the Social Explorer FAQs:
Chicago
Report
Data source. Title of table, dates. Prepared by Social Explorer. permalink URL (date accessed).
Example:
U.S. Census Bureau. Population Density, 1960. Prepared by Social Explorer. (accessed Jul 27 13:58:03 EST 2010).
Map
Title of map, dates. Social Explorer, permalink URL (based on data from <identify data source>; date accessed).
Example:
Population Density, 1960. Social Explorer, (based on data from U.S. Census Bureau; accessed Jul 27 17:16:03 EST 2010).
MLA
Report
Data source. “Title of table, dates.” Social Explorer. Medium. Date posted.
Example:
U.S. Census Bureau. “Population Density, 1960.” Social Explorer. Web. Jul 27 13:58:03 EST 2010.
Map
“Title of map, dates.” Map. Social Explorer. Social Explorer, n.d. Medium. Date posted. (based on data from...)
Example:
“Population Density, 1960.” Map. Social Explorer. Social Explorer, n.d. Web. Jul 27 13:58:03 EST 2010. (based on data from U.S. Census Bureau)
From the Census FAQs:
Dynamically generated tables, maps, and files from American FactFinder:
U.S. Census Bureau; Name of the database or other data repository/source; Name of the person who generates the tabulation; Name of the software package used to generate the tabulation, if known, e.g., "using American FactFinder; URL of the application software's main or first page set off by angle brackets, e.g., <http://factfinder2.census.gov>; Date, within parenthesis, when the user generated the tabulation, e.g., (7 January 2012).
For a reference map in American FactFinder:
U.S. Census Bureau; generated by Jane Smith; using American FactFinder; <http://factfinder2.census.gov>; (12 February 2012).
For a thematic map in American FactFinder:
(Find the specific survey or census, data set and matrix number under the map image):
U.S. Census Bureau; Census 2000, Summary File 1, Matrix P7; generated by Joe Smith; using American FactFinder; <http://factfinder2.census.gov>; (15 February 2012).
Examples:
U.S. Census Bureau; American Community Survey, 2010 American Community Survey 1-Year Estimates, Table GCT0101; generated by John Smith; using American FactFinder; <http://factfinder2.census.gov>; (7 January 2012).
U.S. Census Bureau; Census 2000, Summary File 1, Table P001; generated by Jane Jones; using American FactFinder; <http://factfinder2.census.gov>; (20 February 2012)
U.S. Census Bureau; 2010 Census Summary File 1; Tables P1 and QT-P1; generated by John Smith; using American FactFinder; <http://factfinder2.census.gov>; (12 December 2011).