Backpacking nerd? Read the Outdoor Recreation Participation Report 2012. Pages 50-53 have charts showing the numbers of Americans by age group that are participating in various sports. About 2.5% of Americans went backpacking at least once in 2011. Participation in the sport is holding steady, but decreasing for younger kids.
It’s interesting to contrast it with the Outdoor recreation participation in the United States – projections to 2060. I don’t know what to make of this study’s finding that about 38% of all adults went “backpacking or primitive area camping” in 2008.