Many communities that watched the pandemic unfold in faraway places are now experiencing the crisis firsthand. More than two-thirds of rural counties have confirmed at least one case.

In Idaho, Blaine County had the highest per capita infection rate in the nation, rural or urban. More than 100 attendees at a ski event earlier in the month had tested positive, and dozens of health care workers had fallen ill.

Hundreds of rural counties were seeing their first reported cases. The town of Cynthiana in rural Harrison County appeared to be the epicenter of the crisis in Kentucky.

In mid-March, a cluster of cases emerged in Colorado ski country . Vacation destinations were among the earliest in the rural U.S. to record clusters of cases, but that would soon change.

Almost two weeks later and 3,000 miles away, officials in Grafton County , N.H., announced a positive test for a health care worker who had recently traveled to Italy. At that point, there were just 104 cases nationwide and no other rural counties had reported cases.

This map shows every rural county in America, areas where the coronavirus outbreak initially was slow to spread. Humboldt County in Northern California was the first rural county to report a case , on Feb. 20, a month after the virus first reached the U.S.

Grace Rhodes was getting worried last month as she watched the coronavirus tear through New York and Chicago. But her 8,000-person hometown in Southern Illinois still had no reported cases, and her boss at her pharmacy job assured her: “It’ll never get here.”

Now it has. A new wave of coronavirus cases is spreading deep into rural corners of the country where people once hoped their communities might be shielded because of their isolation from hard-hit urban centers and the natural social distancing of life in the countryside.

The coronavirus has officially reached more than two-thirds of the country’s rural counties, with one in 10 reporting at least one death. Doctors and elected officials are warning that a late-arriving wave of illness could overwhelm rural communities that are older, poorer and sicker than much of the country, and already dangerously short on medical help.

Read more: Coronavirus in the U.S.: Latest Map and Case Count

“Everybody never really thought it would get to us,” said Ms. Rhodes, 18, who is studying to become a nurse. “A lot of people are in denial.”

With 42 states now urging people to stay at home, the last holdouts are the Republican governors of North Dakota, South Dakota, Nebraska, Iowa and Arkansas. Gov. Kristi Noem of South Dakota has suggested that the stricter measures violated personal liberties, and she said her state’s rural character made it better positioned to handle the outbreak.

A view into downtown Fairmont, W.Va. The only hospital in its county closed in mid-March. Kristian Thacker for The New York Times

“South Dakota is not New York City,” Ms. Noem said at a news conference last week.

But many rural doctors, leaders and health experts worry that is exactly where their communities are heading, and that they will have fewer hospital beds, ventilators and nurses to handle the onslaught.

“We’re behind the curve in rural America,” said Senator Jon Tester, Democrat of Montana, who said his state needs hundreds of thousands of masks, visors and gowns. “If they don’t have the protective equipment and somebody goes down and gets sick, that could close the hospital.”

Rural nurses and doctors, scarce in normal times, are already calling out sick and being quarantined. Clinics are scrambling to find couriers who can speed their coronavirus tests to labs hundreds of miles away. The loss of 120 rural hospitals over the past decade has left many towns defenseless, and more hospitals are closing even as the pandemic spreads.

Coronavirus illnesses and deaths are still overwhelmingly concentrated in cities and suburbs, and new rural cases have not exploded at the same rate as in some cities. But they are growing fast. This week, the case rate in rural areas was more than double what it was six days earlier.

Confirmed Cases Per 100,000 People Deaths Per 100,000 People 120 cases 3 deaths Urban counties Urban 80 2 Rural counties 40 1 Rural March 1 March 15 April 1 March 1 March 15 April 1 Confirmed Cases Per 100,000 People 120 cases Urban counties 80 Rural counties 40 March 1 March 15 April 1 Deaths Per 100,000 People 3 deaths Urban 2 1 Rural March 1 March 15 April 1

Deaths are being reported in small farming and manufacturing towns that barely had a confirmed case a week ago. Fourteen infections have been reported in the county encompassing Ms. Rhodes’s southern Illinois hometown of Murphysboro, and she recently quarantined with her parents, who are nurses, as a precaution after they got sick.

Rich ski towns like Sun Valley, Idaho, and Vail, Colo., have some of the highest infection rates in the country, and are discouraging visitors and second homeowners from seeking refuge in the mountains. Indian reservations, which grapple daily with high poverty and inadequate medical services, are now confronting soaring numbers of cases.

Michael Angelucci, a state delegate in West Virginia and the administrator of the Marion County Rescue Squad, said the recent closure of a hospital there is already being felt. Kristian Thacker for The New York Times

In some places, the virus has rushed in so suddenly that even leaders are falling ill. In the tiny county of Early in southwest Georgia, five people have died. And the mayor and the police chief of the county seat, Blakely, are among the county’s 92 confirmed cases. It has been a shock for the rural county of fewer than 11,000 people.

“Being from a small town, you think it’s not going to touch us,” Blakely’s assistant police chief, Tonya Tinsley, said. “We are so small and tucked away. You have a perception that it’s in bigger cities.”

That is all gone now.

“You say, wait a minute, I know them!” she said. “It’s, like, oh my God, I knew them. I used to talk to them. I knew their family. Their kids. It’s a blow to the community each time.”

Even a single local case has been enough to jolt some people out of the complacency of the earliest days of the virus, when President Trump spent weeks playing down the threat and many conservative leaders brushed it aside as politically driven hysteria.

Read more: See Which States and Cities Have Told Residents to Stay at Home

In Letcher County, Ky., which got its first case on Sunday, waiting for the disease to arrive has been unnerving. Brian Bowan, 48, likes the daily briefings by Gov. Andy Beshear, a Democrat, and he is glad for the governor’s relatively early actions to close nonessential businesses. Without them, Mr. Bowan said, “we could have a really bad pandemic. We could be like California or New York.”

In Mississippi, a mostly rural state, the virus had spread to nearly every county by April, with more than 1,000 cases and nearly two dozen deaths reported, causing health care workers to wonder, nervously, when the governor would issue a stay-at-home order. Last week, he finally did, and doctors at the University of Mississippi Medical Center in Jackson breathed a sigh of relief.

“There was this chatter today at the medical center, people saying ‘Oh thank goodness — we need this to get people to realize how serious this is,’ ” said Dr. LouAnn Woodward, the hospital’s top executive.

Fairmont Regional Medical Center in Marion County, W.Va., left , is expected to reopen sometime in the next month with limited services provided by West Virginia University. In Fairmont, W.Va., members of the Marion County Rescue Squad departed on a call this week. Kristian Thacker for The New York Times

While Americans are still divided on whether they approve of how Mr. Trump has handled the crisis, the virus is uniting nearly everyone in the country with worry — urban and rural, liberal and conservative. More than 90 percent of Americans said the virus posed a threat to the country’s economy and public health, according to a Pew Research Center poll conducted from March 19 to March 24.

“Some of the petty things that would be in the news and on social media before have sort of fallen away,” said David Graybeal, a Methodist pastor in Athens, Tenn. “There’s a sense that we are really in this together. Now it’s, ‘How can we pull through this and support one another in this social distancing?’ ”

In Mangum, Okla., a town of 6,000 in the western part of the state, it all started with a visit. A pastor from Tulsa appeared at a local church, but got sick shortly thereafter and became the state’s first Covid-19 fatality.

Then somebody at the local church started to feel unwell — a person who eventually tested positive for coronavirus.

“Then it was just a matter of time,” said Mangum’s mayor, Mary Jane Scott. Before realizing they were infected, several people who eventually tested positive for the virus had moved about widely through the city, including to the local nursing home, which now has a cluster of cases.

Over all in the town, there are now three deaths and 26 residents who have tested positive for the coronavirus — one of the highest infection rates in rural America.

“You’d think in rural Oklahoma, that we all live so far apart, but there’s one place where people congregate, and that’s at the nursing home,” she said. “I thought I was safe here in Southwest Oklahoma, I didn’t think there would be a big issue with it, and all of a sudden, bam.”

Mangum now has an emergency shelter-in-place order and a curfew — just like larger towns and cities around the United States.

Just as New Yorkers have gotten accustomed to Gov. Andrew Cuomo’s daily televised briefings, residents of Mangum have turned to the mayor’s Facebook page, where she livecasts status updates and advisories. On Monday night, it was the recommendation that residents use curbside pickup when going to Walmart, a broadcast that garnered more than 1,000 views in the hour after she posted it.

“Since we have no newspaper, it’s the only way I know to get the word out,” she told viewers, after inviting them to contact her personally with any questions or concerns.

She also has encouraged residents to step out onto their lawns each night at 7 p.m. where she leads them in a chorus of “God Bless America.”

The virus has complicated huge swaths of rural life. Darvin Bentlage, a Missouri rancher, says he is having trouble selling his cattle because auctions have been canceled. In areas without reliable internet access, adults are struggling to work remotely and children are having to get assignments and school updates delivered to their door.

Rural health providers are also challenged. A clinic in Stockton, Kan., turned to a local veterinarian for a supply of masks and gowns. One rural hospital in Lexington, Neb., was recently down to its last 500 swabs. Another in Batesville, Ind., was having its staff members store their used masks in plastic baggies in case they had to sterilize and reuse them. In Georgia, a peanut manufacturer in Blakely donated a washer and dryer to the local hospital for its handmade masks and gowns.

“It’s just absolutely crazy,” said Michael Caputo, a state delegate in Fairmont, W.Va. “Across the country, they’re turning hotels and sports complexes into temporary hospitals. And here we’ve got a hospital where the doors are shut.” Kristian Thacker for The New York Times

The financial strain of gearing up to fight the coronavirus has put much pressure on cash-strapped rural hospitals. Many have canceled all non-emergency care like the colonoscopies, minor surgeries and physical therapy sessions that are a critical source of income.

Last month, one hospital in West Virginia and another in Kansas shut their doors altogether.

“It’s just absolutely crazy,” said Michael Caputo, a state delegate in Fairmont, W.Va., where the Fairmont Regional Medical Center, the only hospital in the county, closed in mid-March. “Across the country, they’re turning hotels and sports complexes into temporary hospitals. And here we’ve got a hospital where the doors are shut.”

For now, there is an ambulance posted outside the emergency room, in case sick people show up looking for help.

Michael Angelucci, a state delegate and the administrator of the Marion County Rescue Squad, said the hospital’s closure during the pandemic is already being felt.

On March 23, emergency medics were called to take an 88-year-old woman with the coronavirus to the hospital, Mr. Angelucci said. Instead of making a quick drive to Fairmont Regional, about two minutes away, Mr. Angelucci said that the medics had to drive to the next-nearest hospital, about 25 minutes away. A few days later, she became West Virginia’s first reported coronavirus death.