The Philadelphia suburbs were the key to Joe Biden’s Pennsylvania victory. Here are the numbers.

In Pennsylvania, a state President-elect Joe Biden won by 81,000 votes — and President Donald Trump won four years ago by 44,000 — every vote mattered.

And Philadelphia’s suburbs delivered.

In Bucks, Chester, Delaware, and Montgomery Counties Biden expanded the total margin of victory by nearly 105,000 votes over what Hillary Clinton amassed in her loss in 2016. That was more than enough to offset the gains Trump made in smaller counties across the state, even despite a somewhat disappointing Democratic performance in Philadelphia.

“If Philly didn’t perform up to all expectations for Democrats, the suburbs did. They really, really did,” said Chris Borick, a political science professor at Muhlenberg College and pollster who heads its Institute of Public Opinion. “If you’re looking for one big thing, you’d go to the Philly suburbs. Those margins … were just off the charts.”

Biden picked up votes in towns all across the collar counties, a coalition of municipalities large and small that includes a wide range of political and cultural communities, according to an Inquirer analysis of precinct- and municipal-level data. The analysis, which examined the results in all 238 municipalities in Bucks, Chester, Delaware, and Montgomery Counties, found that:

Biden’s boost wasn’t just in one kind of suburb. His performance stretched across the region, encompassing Democratic bastions of wealthy, white, and well-educated voters such as Lower Merion, where he picked up the biggest gain in net votes, or Haverford, or Abington — as well as racially and ethnically mixed inner suburbs, such as Upper Darby, which had the second-highest net gain in votes, and Yeadon, which is largely Black and continued to vote heavily for Democrats.

The numbers are eye-popping, but also fit broader patterns: The Philadelphia suburbs don’t stand out because they defy long-term trends or the movement in the rest of the state, but because of those shifts and trends.

It’s not just that the Philadelphia suburbs voted heavily for Biden — they’ve been getting bluer for two decades now. Or that turnout surged everywhere — in all 67 counties, Biden drew more than Clinton, and Trump topped his totals from four years ago. Or that suburbs across the state delivered strong numbers for Biden, including outside Pittsburgh and around smaller cities such as in Dauphin, Cumberland, Northampton, and Lackawanna Counties.

» READ MORE: The Philly suburbs aren’t the only suburbs where Democrats are on the rise in Pennsylvania

It’s the size of the Philadelphia suburbs — and their growing, educated, increasingly racially and ethnically diverse electorate — that makes them key for Democrats. Even relatively small shifts in turnout and vote share can mean a difference of tens or even hundreds of thousands of votes.

That’s what happened this year: Turnout rose as towns shifted left.

Statewide, the number of presidential votes cast rose by more than 13% this year. The votes cast for either the Democratic or Republican nominee in particular rose by 16%.

Delaware County’s two-party vote was up, though below the statewide average, but the other counties exceeded it: Bucks, Montgomery, and Chester Counties each rose close to or just above 20%.

That points to another big difference in 2020: While the Libertarian, Green, and Constitution party candidates won 3.6% of the vote in Pennsylvania four years ago, third-party candidates won just 1.1% in 2020. Notably, the Green Party candidate was removed from the ballot in Pennsylvania.

Overall, the two-party vote in the four counties rose by 18.3% — an increase of 237,000 votes, from 1.3 million in 2016 to more than 1.5 million this year.

That’s a significant number of additional votes. But it’s not enough on its own to explain Biden’s win.

After all, turnout rose in other counties, too. In the 54 counties that Trump won in both 2016 and 2020, the two-party votes increased by 17.8%. That’s a smaller rise than in the Philadelphia suburbs, but it’s a growth of 445,000 votes from 2.5 million in 2016 to more than 2.9 million this year.

That’s where the shift in votes comes in.

Although it’s easy to paint the Philadelphia suburbs with a broad brush, the reality is there are dozens — hundreds — of communities, cultures, and subcultures there, making up a complicated quilt of political leanings. And it was a shift all across those communities that gave Biden huge numbers.

It’s not just turnout that matters, or just the vote share — it’s the combination of the two and the ultimate margin of victory.

Consider Philadelphia. Biden received nearly 20,000 more votes than Clinton did in the deep-blue city. But Trump also received more support in Philadelphia this year — 24,000 more votes.

So even though Biden’s 471,000 votes in the city was more than any past Democratic presidential candidate, and even though Philadelphia still voted heavily Democratic, his net vote, or share of the total cast, was actually lower than Clinton’s.

» READ MORE: Philly was supposed to turn out huge for Biden. It didn’t. What happened?

And those are the numbers that add up, because candidates aren’t starting with a blank map. By taking the 2016 map as a baseline, looking at the difference in votes allows us to see how this election compares.

That’s how Lower Merion, for example, ends up being such a powerful driver of votes. The town was already blue, and shifted slightly left, going from voting 78.1% for Clinton to 79.1% for Biden. The total number of votes cast for either party’s nominee increased by 16%.

That rate is lower than the rest of the suburbs, but because Lower Merion has the largest number of Biden and Clinton votes of any town in the area, the increase in turnout and its leftward shift meant more than 4,000 net votes for Biden. That alone was nearly enough to offset the decreased net Biden votes from Philadelphia.

Despite Biden’s strong performance, Trump clearly retained some appeal in the suburbs. For example, the working- and middle-class towns of Bensalem and Bristol in Lower Bucks County both continued to shift to the right — four years after Trump drew more support there than the GOP nominee in 2012, Mitt Romney.

Biden still won Bensalem and Bristol, but the Democrats’ slide there reflects the party’s broader struggles among white voters without college degrees.

At the same time, however, Biden made inroads in affluent, well-educated, and predominantly white towns that Trump won in 2016. In Central Bucks, for example, Warrington, Warminster, and Upper Makefield all flipped this year for Biden.

» READ MORE: Suburban voters in Pennsylvania rejected Trump — but not the Republican Party

It will be difficult for Democrats to replicate Biden’s dominating performance in the region.

Dave Wasserman, an elections analyst with the nonpartisan Cook Political Report, said Democrats could possibly build on their margins for the next presidential election. At the same time, he said, the party could see more defections beyond the cities and their ring collars from voters who might have liked Biden — but not the Democrats “brand” as a whole.

“So this election,” he said, “points to Pennsylvania continuing to be a highly competitive state in the future.”

Staff writer Chris A. Williams contributed to this article.