This article doesn't mention the religious communities where young people commonly marry and start having children before age 20.
A friend of mine grew up in one such fundamentalist community in rural Iowa; she married at 20, but some of her peers were already moms by that age. I wonder whether they include this type of parent in the statistics, or are they only talking about unwed mothers here?
There seem to be a lot of rural counties in the first quintile of teenage pregnancy, and I venture to guess that some of them, the ones not in large cities or general urban areas, are traditional or fundamentalist communities where teenage girls often marry.
Unfortunately, our socio-economic system (outside these specialized communities) is just not set up to accommodate pregnancy at the age when we are most fertile. It's too bad, given how many of us are delaying having children until our 30s, even 40s, and running into all sorts of issues for both the mom and the child; I have personal experience in this.
Anyway, this looks like a good trend, that kids are either finally "getting it" or else they're simply too distracted by technological toys to be fooling around like they used to!