List the government agency first. In this case, your citation will start with, "U.S. Census Bureau."
Add the year of publication enclosed in parentheses and ending with a period outside the last parenthesis.
Add the title of the publication or report using sentence case and put it in italics.
Add the publication number, if there is one. Government agencies often give their reports a number but this is not always the case. Omit if there is not one. Enclose the number in parentheses and end with a period.
Add the publisher and location if this is a printed report. In this case, the publisher is always the Government Printing Office and it is published in Washington, DC. Your citation would look like this:
Washington, DC: Government Printing Office.
Add "Retrieved from" and the complete URL of the document if you found this publication online. For example, your complete citation might look like this:
U.S. Census Bureau. (2010). Income, poverty, and health insurance coverage in the United States: 2009. Retrieved from http://www.census.gov/prod/2010pubs/p60-238.pdf.