According to the latest US Census Bureau tables (2008, http://www.census.gov/hhes/www/cpstables/032009/rdcall/1_001.htm):
The median American income is
(before taxes and excluding capital gains).
The mean (average) American income is
due to extremely wealthy individuals in the upper quintile pulling the average up.
This information is for HOUSEHOLD income not INDIVIDUAL income. The individual income is a little more than half the household income. The link given above says this. The individual income for people over 18 is under 30k/yr.