The last numbers I saw were somewhere between 1 and 1.5% of the US population, and peanut allergies are one of the most deadly, along with shellfish and venom. My allergist sees a fairly large number of people that are allergic to all three (and more) each day, and that doesn’t include all the other practices in the area. It’s more common than you think.
There is some good news for peanut allergy sufferers coming
http://www.usatoday.com/news/health/2003-03-10-peanut-allergy_x.htm