While Pennsylvania's population remains the 6th highest in the union with 12,702,379 residents, southwest Pennsylvania's population faces decline. According to the 2010 Census results Allegheny County experienced a 4.6% population loss counting for 58,318 people, while Pittsburgh's population dropped to 305,704 from 334,563.
Chris Briem, Regional Economist at Pitt's University Center for Social and Urban Research, says that the declining population is fallout from families migrating after a lot of industry left the region. "The job loss here, the loss of heavy industry here, was about as extreme as you would find even by Rust Belt standards. So I think a lot of those long term demographic trends are impacting us more than elsewhere."
Briem says that once families left the region they took away some of the opportunity for the population to grow and left behind an older population that is less likely to have children.
Other Pennsylvania regions fared better than the Pittsburgh region with the entire state gaining 421,325 people and Philadelphia County acquiring an additional 8,456 people.