I'm not sure that it matters what percentage we are... the numbers I run into most often from those who are "in the know" about temperament suggest about 0.8%-1.0% of the male population are INFJ, and about 1.4%-1.6% of the female population are.
Never trust what's on internet psychology and self-help sites... they tend to be disproportionately populated by INFP/INFJ types... just because this stuff INTERESTS us. By comparison, some types are quite common in the population at large... but you'll barely find ANY evidence of them on the web... because the web barely interests them at ALL, beyond maybe getting a stock quote, or instructions on how to install new brakes in their car.
Denmarkguy