These are of course related. Graybeards like us don't specialize in the violent crimes and handguns and incarceration stats whose lack is considered peace. We stand in line at Red's, not at gun shows. USPI is really talking about safety, I guess, not peace, and "safe" definitely describes Maine, where I'd bet a significant percent of the population leaves doors unlocked. (Most unlocked state in the nation....) I'm not sure about extrapolating from safety to peace. Personally, I give Maine a lot of credit for any ease of mind and belief in nature and quiet contemplation that I might feel, and it feels right (and a little jingoistic) that southern states have the least peace and northeast the most, but peace, like anger or allergies, is probably spread pretty evenly throughout the population irrespective of state lines or national statistics.
I won't argue with the US Census. What I'm having difficulty sorting out is the worth or harm of the age stats: young people leave and take their energy; old people come and bring their money. Maybe it makes no difference, as long as we don't become Fort Lauderdale.