It is surprisingly difficult to find any recent statistics on homeschoolers. The last nationwide survey was in 2003, and it is tough to find anything more current. According to the NCES, "about 1.1 million students ... were being homeschooled in the United States in the srping of 2003", up from an estimated 850,000 in 1999. This reflects an increase in the percentage of children being homeschooled from 1.7% in 1999 to 2.2% in 2003. Extrapolating from this, and figuring on some homeschoolers not reporting openly, the percentage of U.S. children being homeschooled in 2007 is probably closer to 4% than 2%.
Locally, there are 394 elementary homeschoolers in Gallatin County, compared to 7336 elementary kids in the county, or 5% of the total. There are 123 high school homeschoolers (which is probably low, since many high school students are older than 16 and therefore don't have to register), compared to 3183 high school students, or 3.7% of the total. Both numbers are probably a little low because some homeschoolers don't register, especially if they have had problems with homeschooling in other states. But 5% is probably pretty accurate for local numbers.