How many households make up the top 10% of US taxpayers?

The Census Bureau claims that in March 2003 there were approximately
75.6 million households in the US (a household meaning a place of
residence with a person or people using it as their main residence).

The top 10% of households would be 10% of that number... 7.56 million.

So the top 10% of households is about 7,560,000.  However for tax
purposes it's important to note that not all households file their
taxes as 1 unit.  Some houses hold multiple families, others hold
multiple single adults, and then some married people living together
file their taxes separately.  I doubt the IRS publishes any
information on "households" so that terminology can't be very specific
when used in relationship to taxes.