Pennsylvania’s population loss since 2020 occurred mostly in counties Joe Biden won

Newly released Census data show Pennsylvania’s population declines since the last presidential election are mostly concentrated in counties where President Joe Biden won in 2020.

About 45,000 Pennsylvania residents left counties that Biden won, according to the analysis from Franklin & Marshall College. Counties that voted for former President Donald Trump gained 4,500 residents, adding up to a net statewide loss of about 41,000 people from the 13.0 million residents counted during the 2020 census.

The analysis looks at residents, not registered voters, so it’s impossible to deduce whether one party benefits and whether shifts might impact a statewide vote. About half of the residents who left counties that Biden won relocated within the state and half moved to another state.

The analysis reflects population growth trends in parts of Central and South Pennsylvania, known as the “T”, and population losses in the state’s two biggest cities, Philadelphia and Pittsburgh.

“The natural feeling is that Trump counties, rural counties are losing population, but there’s a lot of central Pennsylvania counties experiencing growth that are still Republican counties,” said Berwood Yost, who conducted the analysis.

Typically a state’s demographics don’t change enough in four years to seriously affect a presidential election from one cycle to the cycle. But Pennsylvania’s narrow margins mean that any shift could be magnified.

“We don’t know how many of these people will vote, we don’t know what happens when they move within the state and if they take their views with them,” Yost said. “It’s just another data point that says we knew this race was gonna be close and guess what, you could infer from these movements that it’s probably gonna be even closer than we thought.”

The population decline in counties Biden won was largely due to losses in the state’s two biggest cities. Philadelphia’s estimated population decreased for the third consecutive year in 2023, possibly due to pandemic-related migration. Philadelphia has not declined in population for three years in a row since between 2004 and 2006

Since April 2020, Philadelphia’s population has declined 3.3% — or 53,251 residents, now standing at an estimated 1,550,542 residents.

Allegheny County, which includes Pittsburgh and its outlying suburbs, lost about 26,000 residents over the last four years.

The decline in counties Biden won would be almost twice as large if not for international migration. About 48,000 people have migrated from other countries to Pennsylvania counties that Biden won.

About half of the 45,000 residents who left Biden counties relocated in-state and half left the state, according to Yost’s analysis. That means that there are about 22,500 fewer people living in counties that voted for Biden than there were in 2020. How, or if those people vote, is unknown.

Biden won Pennsylvania by about 80,000 votes in 2020, a little more than 1%. Trump won it by 44,000 votes in 2016, a little less than 1%.

Most of the people who moved out of Philadelphia but stayed in-state moved to the collar counties. Suburban counties like Chester and Montgomery had the largest gains statewide.

Residents who left Allegheny but stayed in-state also sought out the nearest suburbs, moving mostly to Westmoreland, Washington, Beaver, and Butler Counties. But in that case, the suburb-seekers were relocating from a Democratic stronghold to more conservative areas. People move for all sorts of reasons, including sometimes political ideology.

“If you leave Philly and you go to the suburbs, those are still places were Biden performed pretty well,” Yost said. “But if you leave Pittsburgh and go to Westmoreland or Beaver, places where Trump won, are you moving out there to save money or because it’s more in line with your political viewpoints?”

While rural counties have experienced population losses in Pennsylvania and around the country, Pennsylvania is home to a lot of mid-sized cities and exurban areas that are growing in areas like Adams, York, Cumberland, Lebanon, and Berks Counties.

Migration into counties Trump won was significant enough to offset natural population decline in those areas, where there are more deaths and fewer births than in other parts of the state.

The population shifts also reflect voter registration changes in the state. Since 2020, Republicans have narrowed the registration gap with Democrats in the state, according to an Inquirer analysis. Many of those counties where Republicans gained were counties where the population increased.

Democratic-leaning Montgomery, Chester, and Delaware Counties, some of the larger growing counties, were the only places where the net share of registered Democrats also grew.