Due to continually improved life expectancy, and as baby boomers reach retirement age, the median age of the U.S. population has been steadily increasing. The typical American today is 37.6 years old, nearly 10 years older than the median age in 1970. Despite this trend, many areas in the United States have considerably younger populations.

With data from the U.S. Census Bureau, 24/7 Wall St. reviewed the median age in all U.S. counties to identify the county in every state with the youngest residents. Lexington, Virginia — an independent city that is equivalent to a county for the purposes of census tracking — is America’s youngest county. The median age in Lexington is only 21.4 years old.

21. Suffolk County, Massachusetts

> Median age: 32.2
> State median age: 39.3
> Population under 5 yrs. old: 5.6%
> Enrolled in college: 15.3%

In many of the youngest counties, a large share of residents are students attending college. If the county has a relatively small population, this can dramatically lower the median age. This is the case in Lexington, which has the highest share of residents enrolled in postsecondary education. Of the 7,071 residents, nearly 60% are college students. In 41 states, the share of college students in the youngest county is higher than the share across the state.

When the presence of colleges or a major university is not the explanation for a low median age, high shares of families with young children can often explain the youth of a county’s population.
There are nine counties on this list that have a lower share of college students than their state. Each of these counties has a higher share of children younger than 5 years old than the comparable state figure.

Generally speaking, western and southern states have younger populations than midwestern and northeastern states. Because counties tend to roughly mirror statewide trends, even the youngest county in a state can be relatively old in a national context. For example, in Androscoggin, Maine — the oldest state — the typical resident is 40.6 years old. While this is the lowest median age in the state, it is higher than the median age nationwide.

To determine the youngest county in every state, 24/7 Wall St. reviewed the median age for all U.S. counties from the U.S. Census Bureau’s 2015 American Community Survey. The share of residents enrolled in undergraduate, graduate, or professional schools, as well as the share of each county’s population under 5 years old also came from the ACS.

Click here to see the youngest county in every state.