Driving the resurgence are young adults, who are delaying careers, marriage and having children amid persistently high unemployment. Burdened with college debt or toiling in temporary, lower-wage positions, they are spurning homeownership in the suburbs for shorter-term, no-strings-attached apartment living, public transit and proximity to potential jobs in larger cities.

While economists tend to believe the city boom is temporary, that is not stopping many city planning agencies and apartment developers from seeking to boost their appeal to the sizable demographic of 18-to-29-year olds. They make up roughly 1 in 6 Americans, and some sociologists are calling them “generation rent.” The planners and developers are betting on young Americans’ continued interest in urban living, sensing that some longer-term changes such as decreased reliance on cars may be afoot.

The last time growth in big cities surpassed that in outlying areas occurred prior to 1920, before the rise of mass-produced automobiles spurred expansion beyond city cores.