The youngest state in the country is Utah, new data shows.

Utah residents have a median age of 30.7 years old, younger than any other state in the U.S., according to 2016 data from the Census Bureau’s American Community Survey. Alaska, the District of Columbia and Texas follow closely behind — all with median ages under 35. Nationwide, the median age is 37.9, up from 30 in 1980.

Utah’s high birth rate explains its youth, says Tim Heaton, a sociology professor at Brigham Young University. More than half of adults in Utah are Mormon, according to Pew Research Center, which Heaton believes is driving Utah’s population of young people; the state had the second highest birth rate in the country in 2015, according to the Centers for Disease Control and Prevention.

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Not every youthful place has a high birth rate. Washington, D.C., with one of the lowest birth rates in the country, draws its youth from the many young adults who flock to cities.

Some of the oldest states in the country are in the Northeast, with the highest median ages in Vermont, New Hampshire and Maine. “Over the last few decades, more young people and immigrants have moved to the Sunbelt region, in contrast to the low-migration states that are aging more rapidly,” said William Frey, a senior fellow at the Brookings Institution’s Metropolitan Policy Program. Frey calls this the “Snow Belt” (Northeast and Midwest) to “Sun Belt” (South and West) flow, a migration pattern that has picked up since the recession.

Correction: The original version of this story misstated the national median age in 1980. It was 30, not 31.7.

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