Joe Biden was declared the winner of the 2020 presidential election after the Associated Press and other outlets declared him the winner of Pennsylvania. Although the vote margins are close in Wisconsin, Arizona and Georgia, Pennsylvania was the state that tipped the scale enough to call the election.

So, how did he win Pennsylvania? The New York Times attributed Biden’s win to “counties east of the Appalachians [that] shifted left.” The Washington Post argued that “it wasn’t Pennsylvania’s major urban centers that set the result in 2020.” Instead, they wrote, “It was Erie County and other places like it, where relatively minor shifts across a wide swath of small, industrial cities, growing suburbs and sprawling exurbs.”

But if Allegheny County voted for Biden as predictably as it had for Democratic candidates the past five elections, the results this year could still be uncertain. It was Biden’s unusual, historic performance in Allegheny County, alongside one suburban Philadelphia county, Montgomery County, which provided enough of a margin for Biden to definitively win.

As of Wednesday evening, Allegheny County had already recorded the vast majority of its votes, more than 717,000, the largest number of ballots cast since more than 719,000 votes were cast when Lyndon Johnson was elected in 1964. And the 1964 election was near the peak of the county’s population boom when about 30% more people called Allegheny County home. There are still some provisional and overseas ballots that haven’t yet been included and just under 1,000 additional ballots that were postmarked by Election Day and arrived within three days.

PublicSource looked at how each of the 1,323 precincts in the county voted to tell the story of how Biden won. As the last ballots are counted, it could change the results in single precincts that are close. We’ll update this piece with any changes once all the votes are tabulated.

Five takeaways:

  1. Allegheny County was one of two counties in Pennsylvania, along with Montgomery County, where Democratic votes increased enough to give Biden a definitive win.
  2. Both presidential candidates increased the number of votes their party received compared to 2016.
  3. Biden is winning by nearly 146,000 votes, the biggest margin in Allegheny County since 1964. The urban core and most of the suburbs voted for Biden. Trump’s wins came largely on the edges of the county such as in Findlay, Fawn and Elizabeth townships.
  4. Some of the biggest gains for Biden from 2016 were in suburban and rural precincts, some of which he still lost. Some of Trump’s improvements were in primarily Black neighborhoods in the urban core.
  5. While Trump expanded to the urban core, Biden expanded there too, and almost everywhere else,  ultimately winning the county by the largest percentage since 1992.

Allegheny County was one of the two most important counties for Biden

As of Wednesday night, Biden led Donald Trump by 51,301 votes in Pennsylvania, according to the state tally, enough votes to prevent an automatic recount and likely enough votes to survive any legal challenges that Trump attempts. 

Allegheny County delivered around 47,000 more votes for Biden than the average Democratic presidential candidates since 2000. And he won more than 37,000 additional votes compared to Hillary Clinton in 2016. Only Montgomery County moved in Biden’s direction by about the same number of raw votes: he’s winning Montgomery by about 37,000 more votes than Clinton did according to the state tally. Allegheny and Montgomery Counties are the second and third largest counties in the state, less populous than Philadelphia.

Their additional votes make any recount or legal efforts unlikely to change the outcome. Although Biden increased his vote margin in other Pennsylvania counties — Allegheny and Montgomery Counties shifted definitively to secure his victory. 

The last five presidential elections in Allegheny County have had predictable results. The Democratic candidate earned between 56-57% of the vote, the Republican 40-42%. The Democratic candidate won by between 90,000 and 108,000 votes. The average number of votes Democrats gained in those five elections was 98,236. 

That predictability changed dramatically this year: Allegheny County has already delivered at least 145,815 more votes to Biden than to Trump.

If Biden had performed just as well as Clinton in Allegheny County — with all else being equal —  he would be winning the race in Pennsylvania by fewer than 15,000 votes. That likely would have triggered an automatic recount and could have made Biden’s margin more susceptible to legal challenges.

Although Philadelphia voted more overwhelmingly for Biden — where he is winning by nearly 450,000 votes in total Philadelphia’s support for Biden was actually lower than its support for Clinton, who won by more than 475,000 votes.

Based on data available so far, Biden appears to be receiving more votes from white suburban voters, while Trump is picking up a higher share of Black urban voters than last time. 

Biden’s blue wave

Biden’s core support locally is still in Pittsburgh. Biden received more votes in 392 out of 402 precincts in the city. And with few exceptions, Biden’s support carried into the suburbs immediately outside the city, including Mt. Lebanon to the south, Fox Chapel to the north and most of Monroeville to the east. But the outer edges of the county, such as Elizabeth Township, Findlay Township and Fawn Township favored Trump. 

Despite this, Biden also owes his victory in part to increases in support in many of these areas where he lost. Four out of the five precincts where Biden increased his vote total the most were in areas Trump won and where Trump also gained hundreds more votes compared to his performance in 2016. Biden kept pace or nearly kept pace with Trump’s increases in most rural areas.

Trump’s pickups came from rural Allegheny County and historically Black neighborhoods

Trump has received more than 20,000 additional votes in 2020 in Allegheny County compared to 2016. His increased support though was geographically broad: He received more votes in 2020 than 2016 in more than 69% of the county’s precincts.

What changed from 2016 to 2020?

One of the most interesting results of the 2020 election is that Biden gained some of his biggest margins in Trump’s strongholds. And Trump made his biggest gains in Biden’s strongholds. But while Trump made inroads in Pittsburgh’s urban core, Biden made inroads almost everywhere else.

A good example is Richland Township. Trump won all eight precincts in 2016 and still won all eight this year. But Biden gained ground in seven the eight precincts and ultimately picked up 287 additional votes there compared to Clinton in 2016. 

 Notably, Biden not only gained ground but earned enough support to win some of the outlying suburbs that Clinton lost, such as McCandless, Ross, White Oak and Upper St. Clair. 

Correction (11/12/2020): A previous version of this story misidentified the vote totals in several precincts in story text and maps. Our story initially was based on a comparison of vote data and precinct boundaries that were mistakenly matched alphabetically. That mistake in matching did not impact every geographic area, but it meant that some voter data was incorrectly attributed to the wrong precinct. Examples based on incorrect data have been removed from the story, and vote totals in the text and maps have been revised to reflect Allegheny County’s voting data current as of November 12. We sincerely regret the error.

Oliver Morrison is PublicSource’s environment and health reporter. He can be reached at or on Twitter @ORMorrison.

This story was fact-checked by Matt Maielli.

Know more than you did before? Support this work with a MATCHED gift!

Through Dec. 31, the Wyncote Foundation, Loud Hound Foundation and our generous local match pool supporters will match your new monthly donation 12 times or double your one-time gift, all up to $1,000. Now that's good news!

Readers tell us they can't find the information they get from our reporting anywhere else, and we're proud to provide this important service for our community. We work hard to produce accurate, timely, impactful journalism without paywalls that keeps our region informed and moving forward.

However, only about .1% of the people who read our stories contribute to our work financially. Our newsroom depends on the generosity of readers like yourself to make our high-quality local journalism possible, and the costs of the resources it takes to produce it have been rising, so each member means a lot to us.

Your MATCHED donation to our nonprofit newsroom helps ensure everyone in Allegheny County can stay up-to-date about decisions and events that affect them. Please make your gift of support now.

Oliver Morrison is a general assignment reporter at WESA. He previously covered education, environment and health for PublicSource in Pittsburgh and, before that, breaking news and weekend features for...