The U.S. population grew by less than 1% last year, among the slowest rates in decades. Metropolitan areas continue to grow faster than rural areas. Still, among the nation’s 381 metropolitan areas, populations fell in 102.

The U.S. population has grown by 3.7% since 2010. Farmington, New Mexico was the fastest shrinking city, with a population decline of 10.1% over five years.

Population declines are often caused by negative natural growth — when deaths outpace births. While many of the cities on this list indeed have negative natural growth, it is migration — people moving away from these areas to other parts of the country or to other countries — that drove the population to decline in these areas.

Click here to see America’s fastest shrinking cities.

Click here to see America’s fastest growing cities.

The metropolitan areas with the biggest population declines tend to be in the Northeast or the Midwest, particularly in the Rust Belt. Once the manufacturing backbone of the nation, Rust Belt economies have endured decades of steady industrial decline, leading to high unemployment and poverty.

In an interview with 24/7 Wall St., William Frey, senior demographer at public policy think tank Brookings Institute, explained that the continued departure of residents from these metropolitan areas is not surprising for several reasons. The first is that employment opportunities tend to drive population migration, and these cities tend to have weak job markets.

Jobs are perhaps the single most important driver of urban expansion, and the relatively weak job markets and low income levels in these areas mean there are fewer economic opportunities. Such opportunities often attract new residents and encourage current residents to stay.

The unemployment rate in all but one of these 20 metro areas exceeds the national January jobless rate of 4.7%. The average income is also lower than the national per capita income of $47,615 in all but one of the 20 metros.

The relationship between unemployment and population growth is a self-perpetuating cycle, Frey explained. If young people are disinclined to move to an area because it has fewer job opportunities, the population will stagnate, potentially leading to even greater economic decline, and greater job losses.

The metro areas with shrinking populations also tend to have extremely low property values. The typical U.S. home is valued at $173,600. None of the 20 fastest shrinking cities have a median home value above the national figure. In 10 of the 20, the median home value is below $100,000.

Frey explained that home values are in part determined by the desirability of the housing market, and low prices are a sign that few people want to live in these areas.

Young people represent the largest share of the U.S. migratory populations. For this reason, the populations of many of the cities with the fastest shrinking populations are disproportionately old. Nationwide, 27.5% of the U.S. population is 55 and older. In only three of the 20 cities on the list is the share of this age group smaller, and in 14, at least 30% of residents are 55 or older.

24/7 Wall St. based this list of the fastest growing and shrinking cities on recently released U.S. Census Bureau estimates of population changes in the 381 U.S. metropolitan statistical areas from July 2011 through July 2016. Poverty rates, educational attainment rates, and workforce composition came from the Census Bureau’s 2015 American Community Survey. Unemployment rates are for January 2011 and January 2017.

These are America’s fastest shrinking cities.