Here is the information IRS is reporting for fiscal year 2003:
Total Individual Returns filed 130,728,360
Total Estate & Trust Income Tax Returns filed 3,688,043
Total Partnership Returns filed 2,380,618
Total Corporate Returns Filed 5,890,821
Total Estate Tax Returns Filed 91,679
Total Gift Tax Returns Filed 287,456
Total Employment Tax Returns Filed 29,916,033
Total Tax Exempt Organization Returns filed 789,381
Total Excise Tax Returns filed 812,483
To see this information broken down by state, and some additional information
and footnotes, you can read this report:
Number of Returns Filed by Type of State, Fiscal Year 2003, issued in March 2004
Search method - I went to the IRS site www.irs.gov and clicked on Tax Stats,
then, selected the Statistical Overview option
You'll find all kinds of free IRS statistics on their site.
You can really get lost in all the information there.
Incidentally, if you are writing an article, if you are a reporter,
IRS's public affairs officers (Communications, I think they call it)
are very helpful.