That’s because younger residents just beginning their careers make up the foundation of a tax base that can support older workers who have retired or will soon do so. And a decade of dramatic internal migrations away from Northeastern states and toward the Sun Belt and the Mountain West is putting shrinking those tax bases into the spotlight.

Today, eight of the top 11 states with the oldest populations are in the Northeast. The median age in Maine is 42.7 years old; in Vermont and New Hampshire it’s above 41. West Virginia’s population has aged precipitously, too, with a median age of 41.3 years, 8.4 years older than it was in 1990.