+1, Oak.
It's rare to see a cyclist without a helmet around where I live, except, when you see a parent riding along with a child. The kid always has a helmet, but not the parent. I really don't get that. You make the kid wear a helmet because it's the law and you don't want him/her to get a head injury. But, it's OK for you to get TBI?
The closer to the city you get, the more helmet-less riders you see. Sometimes, when I walk out of the university building, to the subway (one block), I see about 25 helmet-less riders go by, to about 5 with helmets. Not just students, either.
About 16 years ago I was toodling along down the road by our rented cottage in Dennisport, Cape Cod. My kids were riding behind me, about maybe 9 and 11 at the time. I so clearly remember 2 older women, from NY, walked by us and commented that, "those helmets must be a new thing required in Massachusetts. We don't do that."