A million is not quite realistic. It is well over 25 million.
Still, this question needs to be clarified. Do you mean how many business are operating, or how many are owned and operated in the united states? Do you mean corporations, or are you going to include non-profit ventures as well.
Do you mean all companies, including sole-proprietorships that are not registered as corporations? This will skew any results you are interested in.
According to the IRS, based on tax return information, there were over 28 million companies in 2004(Corporations, Partnerships and Nonfarm Sole Proprieterships).
According to the Office of Advocacy, as of 2006 there were 26.8 million.
Hope that helps.
28,695.50