For 361 days a year, the old McAllister Farm outside Manchester, Tenn., is a quiet, uninhabited patchwork of fields and trees. But for four days every summer, the farm morphs into the sixth-largest city in the state of Tennessee, packed tight with nearly 100,000 people. That’s because the 750-acre farm is home to Bonnaroo, a massive annual concert event that’s become a mecca for music lovers around the globe.

Bonnaroo is big. Really big. Since it debuted in 2002, it has become the largest festival of its kind in North America -- bigger than Lollapalooza, Coachella and Burning Man. Rolling Stone has called Bonnaroo “the ultimate over-the-top summer festival.” Every year, a sold-out crowd of approximately 80,000 concertgoers descends on the farm outside Manchester, along with another 5,000 or so guests and crew members, and thousands more volunteers. Most of the attendees camp on the farm, but hotels for miles around are also booked solid a year in advance.

All that can be more than a little overwhelming for the small town of Manchester, a sleepy burg of about 10,000 people, about 65 miles southeast of Nashville. When Bonnaroo’s not around, Manchester has the lazy feel of Anytown, U.S.A., with a placid little courthouse square at one end of the main drag and a string of fast-food chains out by the interstate. Hosting a large-scale event is a challenge for any city, but it’s particularly daunting when a festival’s arrival means a tenfold increase in the local population. Handling the onslaught of traffic, crime and health needs of that many people is an art form for local officials. The event this June marked the concert’s 10th anniversary, and officials say the past decade has been an extended course in crowd control.

“Bonnaroo is a lot of work,” says Manchester Mayor Betty Superstein. “But it’s a lot of fun. And the community really has kind of embraced it.”

The big reason residents have come to love the Bonnaroo ballyhoo is the concert’s financial impact -- the event pumps $20 million a year into the local economy. In addition, the concert has contributed more than $1 million to charity groups in Manchester and surrounding Coffee County. Earlier this summer, for example, the town saw the opening of a new amphitheater funded entirely through contributions from Bonnaroo. There are other business impacts, too: The large-scale stage construction company that builds the venues for Bonnaroo recently relocated from Los Angeles to Coffee County, and three new hotels have opened in Manchester in the past two years. “I can’t see why three new hotels would go up except for one reason,” says Superstein. “And that’s Bonnaroo.”

Still, the sheer size of the event means lots of work for local officials. “For Bonnaroo week, everybody’s got a duty,” says Manchester Commissioner of Safety Ross Simmons, who heads up the city’s police and fire departments. Managing the arrival of the concert, he says, is like coordinating with a neighboring town. “It’s a hayfield most of the year, but once they get set up, it’s kind of amazing. Bonnaroo is a city within itself.”

Ask any local official about the first year of Bonnaroo, and you’ll get a universally negative response:

“Horrible,” says Superstein.

“Awful,” says Simmons.

“A nightmare,” says Coffee County Sheriff Steve Graves.

They’re referring to the traffic, which was by all accounts, epically bad. The concert that year had only one entrance -- at the end of a narrow two-lane road. Traffic was brought to a standstill for miles. The trip from Nashville, which normally takes about an hour, stretched into a 16-hour slog. Interstate 24 became a parking lot. Superstein, whose house sits on a hill overlooking the interstate, remembers watching from her front porch: “I could see people stopped on the interstate, get out, walk up to the Waffle House, eat, go back and get in their car, and nothing had moved. They set up picnics in the median.”

The problem, officials all agree, is that they simply didn’t think so many people would actually come. “We didn’t believe them when they said 80,000 people were going to show up,” says Superstein. “Here? In Manchester?”

Today, the traffic flows smoothly. The venue now has six separate entrances and multiple roadways dedicated to concert traffic. City police and the county sheriff’s office coordinate to manage the flow. They bring in state troopers to help direct traffic. There’s now even a temporary interstate exit that’s dedicated solely for Bonnaroo-bound drivers. “Now, everything’s running as smoothly as it can,” says Graves.

Once the event is in full swing, the traffic subsides and officials turn their attention to the other persistent issue: crime. Graves sets up a full-scale mobile command center in a small field just outside the Bonnaroo site. There, his team can respond to calls within the concert venue, and arrest and process offenders on site before transporting them to jail.

Mostly, though, they wait. Over 10 years of Bonnaroo, Graves says he’s learned that it’s often best to let the concert’s private security handle the problems before turning offenders over to the sheriff. “We answer calls inside on a need-to basis,” he says. “If a private security guard goes up to someone and has to take them out, there’s usually not a problem. But if a police officer goes in and takes them out, it can cause a riot. So we try to let their security handle it. If they can’t, we’ll go in.”

The majority of offenses involve drugs and domestic fights. Unsurprisingly, the problems tend to escalate as the event stretches into the third and fourth days. “The heat gets to a lot of people,” Graves says -- it is June in Tennessee, after all. “The crimes usually progress as the concert goes on.” When it comes to narcotics, Graves says his team focuses most of their energy on drug dealers, particularly those who are pedaling lethal substances. “Believe it or not, there’s a lot of fake drugs. There’s a lot of people who come here just to rip kids off. Those are the ones that cause the majority of the problems.”

Inevitably, the combination of heat, drugs and alcohol can have fatal consequences. Ten people have died in the 10 years of Bonnaroo, including two deaths this year. Predictably, the causes have included heat stroke, drug overdoses and injuries from auto accidents. For the most part, though, Graves and other officials say the concertgoers are just there to have a good time. “Most of these kids who come here for the concert are no problem at all,” Graves says.

Mayor Superstein agrees. “All the kids are easygoing. It’s a really mellow crowd.”

Still, hosting an event like Bonnaroo isn’t easy for city and county workers. One sheriff’s deputy, when asked what it takes to put on a concert like this, laughs and answers with just one word: “Miracles.”