Early Inauguration Day morning, she slipped into her pandemic-era work clothes of gray sweatpants and white shirt and ground the beans. Then, with her mug of coffee, she watched on her kitchen television as the green-and-white helicopter took air, removing from the White House grounds the outgoing 45th president of the United States, Donald J. Trump.

In that kitchen, in a brick Colonial house in Watertown, Mass., tears came to the eyes of the woman, Karolyn Kurkjian-Jones. Tears of unabashed joy.

“It’s over, it’s over, it’s over,” Ms. Kurkjian-Jones, a retired kindergarten teacher and pandemic-furloughed concierge at the Boston Park Plaza hotel, said later. “He’s gone.”

Since the election in November of Joseph R. Biden Jr. as the 46th president, a great deal of attention has been paid to the conspiracy theories of Republicans who supported Mr. Trump — especially those who, heeding his combustible words about a stolen election, overran the Capitol in a surge of violence and vandalism on Jan. 6.

But so many more Americans, nearly 81.3 million of them, are like Ms. Kurkjian-Jones, people who voted for Mr. Biden and against Mr. Trump. And, on Wednesday, exactly two weeks after the attack on the Capitol, they celebrated with liquor and baked goods, with Zoom calls and “Amazing Grace” and tears of joy, a new day: a day in which a nation pushed a reset button.

In Chicago, not far from a bakery doing a brisk business in inauguration-themed treats — a Wonder Woman cake featuring the face of Vice President Kamala Harris, for example — Sarah Rassey, 40, made plans to watch the inauguration with her daughter, Madeleine, who also happened to be turning 5.

“I feel lighter,” Ms. Rassey said of Mr. Biden’s presidency. “I’m just grateful, relieved, happy — and, honestly, I’ve been crying tears of joy since last night.”

In Texas, a pair of sisters — both special-education teachers from Killeen — drove more than an hour to be in front of the State Capitol in Austin in time to watch the inauguration on a cellphone. Norma Luna, 49, and Sylvia Luna, 43, were there in part to honor a third sister, Veronica, 56, who died of the coronavirus on Election Day.

“It’s a relief,” Norma Luna cried as she watched the ceremony. “I didn’t think we could get here. We’re proud to be Americans again.”

In Annandale, Va., Isra Chaker, 30, an advocate for refugees and asylum seekers at Oxfam America, felt unburdened of the need to justify her “Americanness” during the Trump administration — even though she was born and raised by Syrian immigrants in Boulder, Colo.

“Today I know that I belong here,” Ms. Chaker, a Muslim who wears a hijab, said. “It was reaffirmed that we are all America and America is all of us.”

And at the Calamari’s Squid Row restaurant in Erie, Pa., vodka was the noontime alcohol of choice among some women who call themselves the Drinking Girls. Mary Jo Campbell, 70, a retired university professor and an official in the Erie County Democratic Party, was there, along with her friends Linda, and Kathy, and Alice, and Cheryl, and Karen, and Amy, and Emily — a band assembled in commiseration after Mr. Trump’s election in 2016.

They removed their masks to sip in jubilation. They cheered the moment that Mr. Biden assumed power. They joined Garth Brooks in singing “Amazing Grace.” And then they sipped some more.

“Everybody was hooting and hollering,” said Ms. Campbell, 70, who wore Ruth Bader Ginsburg earrings to offset her blue “Pennsylvania for Biden” T-shirt.

This inauguration seemed to represent more than the routine transition of power from one political party to another. The smashing of norms by Mr. Trump, culminating with his refusal to concede an election he lost and then his incitement of his supporters to march on the Capitol — leading to indictments and his second impeachment — made the moment seem seismic: a shift from one distinct era to another, with the question of who we are as a republic suddenly open to debate.

In Berkeley, Calif., a software engineer named Martin Turon walked his labradoodle past the Thousand Oaks Elementary School, where a custodian had hung a congratulatory banner featuring an alumna: Vice President Kamala Harris. Mr. Turon said he was very proud of Ms. Harris, but the overarching emotion he was feeling was relief, not jubilation.

“Do you really celebrate right after a big earthquake, when everything is broken?” Mr. Turon asked. “When you’re picking up the boards and the rubble off the streets?”

Indeed, there were small spasms of dissent by those who still do not accept Mr. Biden as the duly elected president, although reporters and members of the National Guard far outnumbered protesters outside state capitols. But then this was a day when those who did recognize the legitimacy of the election — that is, most of the country — marked the moment.

The changeover actually began hours earlier, when Mr. Trump and his wife, Melania, emerged — his extra-long red tie, her dark sunglasses — from the White House to board the Marine One helicopter, only to appear shortly afterward at Joint Base Andrews to address a small crowd of loyalists. As Mr. Trump recited what he said were the accomplishments of his administration — a recitation punctuated by a vow to “be back in some form” — the array of American flags, stirred by the morning breeze, seemed restless.

Meanwhile, in a Massachusetts town 430 miles to the northeast, the retired kindergarten teacher, Ms. Kurkjian-Jones, harbored strong feelings of good riddance.

After Mr. Trump’s swearing-in in 2017, Ms. Kurkjian-Jones began a four-year ritual of sending a colorful postcard to the White House every day except Sunday that said “Donald Trump Release Your Taxes” — which he never did. She always signed the card with her name and the initials ABM — “for ‘America’s Big Mistake,’” she said.

Now, at about noon, Ms. Kurkjian-Jones raised a glass of Moët Champagne in toast to the swearing-in of his successor. “A long time coming,” she said.

Many still believe Mr. Trump’s baseless contention of widespread electoral fraud. The aftershocks of the Capitol attack included a militarized lockdown for the inauguration ceremonies. And the pandemic, which has claimed more than 400,000 lives in the United States, required the nonstop attention of overworked health care workers across the country.

As the inauguration unfolded in Washington, the life-or-death struggles continued at the Martin Luther King Jr. Community Hospital in South Los Angeles. “I’m so tired of zipping black body bags,” a nurse, Amanda Hamilton, said as the distant ceremony continued. “It’s exciting we have a president who actually cares and might do something about it.”

Seconds later came the call of a “Code Blue”: a woman in her early 50s whose heart had slowed and oxygen had plummeted. Ms. Hamilton rushed down the hallway to help insert a breathing tube.

Still, these realities could not suppress for some the day’s sense of profound relief.

Karin Wraley Barbee, 48, an English professor at Siena Heights University in Adrian, Mich., said the day felt like a bookend to the day after Mr. Trump won in 2016, when she taught classes at the university but felt she could burst into tears at any time.

“I’m not naïve enough to think everything is OK; it’s not,” she said. “Everyone is very, very awake, and invested in repairing what was damaged.”

Mr. Barbee finished teaching a composition class at 11:50, then ran to her office, where she managed to catch the swearing-in of the new president on her computer. She could hear a few colleagues clapping in the moment. And then, she said, “A couple of us did a little dance.”

Reporting was contributed by Ellen Barry, Julie Bosman, Sheri Fink, Thomas Fuller, Miriam Jordan and David Montgomery.