According to the Bureau of Labor Statistics, more than 1.8 million civilians work for the Federal Government, excluding the Post Office. Below is a link to the relevant BLS website, lots of good information.
Credible sources believe that the number of government contractors outnumber government employees. No one really knows how many government contractors there are.
http://www.bls.gov/home.htm
700,000 employees at the post office of 2006
226,662 work for NY state, Illinois - 105,892, CA - 335,971, TX - 284,729 and so on
Fed - 1.8M
USPS - .7M
Cons - 1.8M
States - 5M
Folks that is almost 10 million people working for the government and that does not count 1.5M people on active duty in the military, with an additional 848,000 people in the seven reserve components.
The total US workforce is 156M.