People across the country will be watching Pennsylvania on election night for any signs of which way the pivotal battleground state will tip.

It could take days to get the full results. But there are some key places we’ll be eyeing for clues about how the race is unfolding, whose voters are turning out, and whose aren’t.

If Democratic votes surge in one suburb, it’s a good bet that’s happening in others.

If blue-collar Trump supporters again pour out in huge numbers in one rural county, odds are the pattern will be repeated with similar voters elsewhere.

With 9 million voters and 67 counties in Pennsylvania — and 20 Electoral College votes at stake — here are some of the key places where you can take the temperature of a state that could decide whether President Donald Trump or Democrat Joe Biden wins the election.

The Philadelphia suburbs

Just how bad will it get for Trump in the Philadelphia suburbs? In 2016, Hillary Clinton outperformed President Barack Obama’s 2012 performance in the city’s four collar counties, beating Trump by about 188,000 votes. Democrats think Joe Biden can do even better, running up the score so much in these populous counties that it might be impossible for Trump to overcome the deficit.

Chester County

Chester County voted for Mitt Romney in 2012 before backing Hillary Clinton in 2016 by about 10 percentage points. Since then, Democrats have made historic gains in what had long been a GOP stronghold, winning federal, state, and local offices.

If Biden can build on Clinton’s margins, this is one place it could happen.

Bucks County

Although other collar counties have turned reliably Democratic, Bucks is still contested. Trump held his own in Bucks four years ago, losing by less than 1 percentage point. It tends to be a swing county in presidential elections, and local GOP officials say enthusiasm for Trump is high. But there are also signs Trump may be struggling there.

If so, that’s trouble for the president.

The swing counties

One of the keys to Trump’s 2016 victory was his appeal to white, working-class voters in areas that had been longtime Democratic strongholds. Several counties in these areas voted twice for Obama and swung heavily to Trump — and he’s aiming for even bigger wins in the same places this time around.

Will the Obama-Trump voters stay with the president this time? And even if they do, will Democrats who sat out the 2016 election come back for Biden?

These counties will offer some clues.

Luzerne County

Trump’s 26,000-vote edge over Clinton in this Northeastern Pennsylvania county accounted for more than half of his total margin of victory in the state. In terms of raw votes, it saw the biggest swing toward Trump of any county in the state. It was one of three counties in the state, along with Erie and Northampton, that twice backed Obama before voting for Trump.

Since 2016, the GOP has outpaced Democrats in voter registrations and won control of the county council.

Lackawanna County

Luzerne’s neighboring county was home to the second-biggest swing toward Trump, even though Clinton still carried it narrowly. Biden’s childhood hometown of Scranton is in Lackawanna — just one reason Democrats think he’s better positioned to ease losses here and win the state.

Erie County

Erie, in the state’s northwestern corner, is seen by both parties as a bellwether for Pennsylvania as a whole. It’s a microcosm of the industrial Midwest, and perhaps Biden’s best shot to win back an Obama-Trump county. It will provide another clue about whether voters who swung to Trump stay with him.

Conservative strongholds

In 2016, Trump won by huge margins in rural and exurban areas and small towns that were already conservative. As his campaign stop last week in deep-red Altoona showed, he’s hoping to squeeze even more votes out of these areas.

The three counties below gave Trump his biggest 2016 victories in terms of raw vote count. Will their numbers go up or down for the president?

Visitors stop at the “Trump House” in Youngstown, in Westmoreland County, in September.
TOM GRALISH / Staff Photographer
Visitors stop at the “Trump House” in Youngstown, in Westmoreland County, in September.

York County

York, in south central Pennsylvania’s Dutch Country, is one of Republicans' most powerful vote centers. In 2016, it gave Trump his biggest win of any county: a 60,000-vote margin.

Westmoreland County

Trump won Westmoreland County, a historically Democratic area in Southwestern Pennsylvania that had been trending Republican for years, by a 2-1 ratio. GOP voter registrations jumped more than 10% from the 2016 primary election to the 2020 primary, while Democratic registrations plummeted.

Lancaster County

Like York, it’s one of the more populous places that votes strongly Republican. Trump won it by almost 50,000 votes last election, and its population has been growing. The campaign has held several major events here, including a Trump rally last Monday.

The liberal strongholds

There’s no question that Biden will win Pennsylvania’s two biggest urban centers, Philadelphia and Pittsburgh.

The question is by how much.

Philadelphia

Clinton won almost as many votes in Philadelphia as Obama did in 2012. Can Biden match that turnout or even do better? Black voters said in interviews this fall that although they may not be jumping up and down to vote for Biden, they’re eager to oust Trump.

Meanwhile, Trump’s campaign has been trying to siphon off votes among Black men, who overwhelmingly lean Democratic — but less so than Black women.

Allegheny County

Allegheny County, where Pittsburgh is located, is the lone Democratic stronghold in Southwestern Pennsylvania. Democrats see an opportunity for Biden to carry not just Pittsburgh, but also the historically Republican suburban towns north of the city that have soured on Trump since 2016.