By the numbers: The share of Americans who moved in the past year is about half of the number in the 1950s, when about one-fifth of the population moved each year. That number is now 9.8%, the first time it’s dipped below 10%.

• Only 20% of people aged 20-24 moved this past year, down from 29% in the 2005-06 year.
• Of those in their late 60s, only 4% moved in the past year.
• 19.7% of renter households (who tend to be more mobile than homeowners) moved, down from 30.2% in 2005-06.

What they’re saying: “There’s been this long term decline in mobility going back to the 1950s, as the population got older and as more people owned houses in the ’60s and ’70s and didn’t move,” said demographer William Frey of the Brookings Institution. “But the continued decline since the Great Recession and the housing crunch is driven by the millennial population.”

The big picture: Decades ago, job markets were more interchangeable and diverse, so it was easier for people with most occupations, from factory workers to bankers, to find jobs in a variety of places that were relatively affordable. Now, though, industries are clustered in specific regions, middle-class jobs have declined, and housing prices are rising in many prosperous areas.

• As a result, low-wage and high-wage workers have less flexibility to relocate.
• Long-distance migration — across the country, for instance — tends to happen more among the more highly educated population drawn to new cities by jobs.
• Short-distance migration, often within the same county, is usually due to housing-related reasons.

Between the lines: The fact that far fewer people are moving to new counties or states could be a bad sign for economic mobility, per research by McKinsey Global Institute.

• When people do move, they go to places that are very similar to where they came from.
• Those living in cities move to other cities or suburbs, and rural dwellers usually stay rural.
• That means people from distressed areas aren’t finding their way into more prosperous ones, leading to sustained economic gaps between places.

What to watch: It’s also a bad sign for smaller cities and rural areas that are already having trouble attracting new residents. Stagnating areas are likely to stay stagnant if people feel stuck in place.

What’s next: Immigrants are contributing significantly to population growth, and Frey predicts first- and second-generation immigrants may drive an increase in mobility going forward.