Here is the most current official data I could locate anywhere:
According to the U.S. Small Business Administration (SBA), 53% of the
25.8 million small businesses in the USA are home-based. This equals a
number of 13.674 million home-based businesses.
In their 2006 study "The Impact of Location on Net Income: A
Comparison of Homebased and Non-Homebased Sole Proprietors", the
SBA provides more information:
"Homebased sole proprietors who take the home business deduction
contribute a total of $102 billion in revenue to the economy. The 10
million 'all other' firms, which appear to be largely homebased,
contribute an additional $431 billion."
In the study, the approximate total number of home-based sole
proprietor businesses is given as 2,217,208. Together with the
additional 10 million home-based businesses, the number of 12.2
million businesses comes close to the very rough estimate mentioned
So there are about 12.2 home-based businesses with a total annual
revenue of $533 billion.
Hope this data will be useful for you!
 U.S. Small Business Administration: Frequently Asked Questions
 U.S. Small Business Administration: The Impact of Location on Net
Income (May 2006)