As the United States continues to get grayer around the ears due to the aging Baby Boom generation, a few states have gotten younger as a result of oil production.

Nationally, the median age in the United States rose slightly from 2012 to 2013, from 37.5 years to 37.6 years, according to new figures released by the Census Bureau.

Baby boomers were responsible for this shift, pushing the size of the senior population up by 3.6% last year. There are now 44.7 million Americans 65 and older.

Meanwhile, seven states experienced a drop in their median age during the same span.

Some of this decline was attributed to the oil and gas rush that’s been taking place in the Dakotas, Montana, Wyoming and Oklahoma since hydraulic fracturing opened up previously untapped reserves. Demand for drillers and other industry workers has prompted many younger Americans, mostly men, to relocate to these states for employment.

North Dakota, home to the Bakken shale oil boom, witnessed the largest drop in average age by 0.6 years between 2012 and 2013. Similar, though smaller declines also occurred in Montana, Wyoming, South Dakota and Oklahoma. Alaska and Hawaii also got younger.

 “We’re seeing the demographic impact of two booms,” John Thompson, director of the Census Bureau, said in a press release. “The population in the Great Plains energy boom states is becoming younger and more male as workers move in seeking employment in the oil and gas industry, while the U.S. as a whole continues to age as the youngest of the baby boom generation enters their 50s.”

-Noel Brinkerhoff

To Learn More:

As the Nation Ages, Seven States Become Younger, Census Bureau Reports (U.S. Census Bureau)

Table 1. States with a Decline in Median Age: July 1, 2012 to July 1, 2013 (U.S. Census Bureau)