To identify the youngest county in each state, 24/7 Wall St. reviewed the median age of each U.S. county from the U.S. Census Bureau’s 2017 American Community Survey. Data on the share of residents under 18 years, the share under 5 years, and population changes also came from the ACS. In Alaska, county equivalents are referred to as boroughs or census areas, and in Louisiana, parishes are county equivalents. In counties without a county seat, the most populous city is listed. In our analysis, we included independent cities, which the Census categorizes alongside counties. In counties without a county seat, the most populous city is listed. We did not list a county seat of most populous city for independent cities.