WASHINGTON — A record number of US counties — more than 1 in 3 — are now dying off, hit by an aging population and weakened local economies that are spurring young adults to seek jobs and build families elsewhere.
New 2012 Census estimates released Thursday highlight the population shifts as the US encounters its most sluggish growth levels since the Great Depression.
The findings also reflect the increasing economic importance of foreign-born residents as the US ponders an immigration law overhaul. Without new immigrants, metropolitan areas such as New York, Chicago, Detroit, Pittsburgh, and St. Louis would have posted flat or negative population growth in the last year.
With a slowly improving US economy, young adults are now back on the move, departing traditional big cities to test the job market mostly in the South and West. Also seeing big declines now are rural and exurban areas, along with industrial areas of the Rust Belt.
Census data show that 1,135 of the nation’s 3,143 counties are now experiencing ‘‘natural decrease,’’ where deaths exceed births. That’s up from roughly 880 US counties, or 1 in 4, in 2009.
By region, growth in the Northeast slowed last year to 0.3 percent, the lowest since 2007; in the Midwest, growth fell to 0.25 percent, the lowest in at least a decade. In the South and West, growth rates ticked up to 1.1 percent and 1.04 percent, respectively.
In the last year, deaths exceeded births in Maine and West Virginia .