Towns include: Castle Rock,
Highlands Ranch,
ParkerLife expectancy at birth: 80.31 years
Douglas County has a long ranching history but is now largely a bedroom community of Denver. The longevity of its citizens goes hand in hand with wealth: This is one of America's richest counties, with huge job and population growth and a vanishingly low poverty rate.
That's not the whole story, of course. This is the Rockies, and outdoor recreation is a big deal. The coast-to-coast American Discovery Trail passes right through Douglas, and the hugely popular Elephant Rock Ride welcomes cyclists of all ages for courses ranging from 8 to 100 miles.
NEXT: 12. San Mateo County, CA (tie)