Authorities say at least 527 others were injured in the attack, including several Southern California residents.
The gunman was identified by police as 64-year-old Stephen Paddock. Police said he fired from the 32nd floor of the Mandalay Bay Hotel and Casino onto the Route 91 Harvest Festival Sunday night.
PHOTOS: Mass shooting in Las Vegas
Officers were able to determine the shots were coming from the 32nd floor of the hotel, and they stormed the room and found the suspect had killed himself, authorities said.
Paddock was found dead in the hotel room with as many as 23 firearms, mostly rifles, varying in caliber.
Authorities said he likely killed himself before officers made entry.
Before the officers made entry, Paddock shot at hotel security through the door, injuring one security officer in the leg, according to Sheriff Joseph Lombardo.
The gunman is from Mesquite, Nevada, just outside of Las Vegas. They described him as a "lone wolf" and do not believe there are other suspects involved in the shooting.
"We believe Paddock is solely responsible for this heinous act," said Asst. Sheriff Todd Fasulo. "We are aware of the rumors outside of the media and also on social media that there was more than one assailant.
We have no information or evidence to support that theory or that rumor. We believe there was only one shooter and that was Stephen Paddock."
Authorities searched his Mesquite home and seized an additional 19 firearms, as well as explosives, several thousand rounds of ammunition and electronic devices.
They also found the fertilizer compound ammonia nitrate, which can be used to make explosives, in his car.
A SWAT team also breached another home in Reno associated with the suspect, officials said.
The Islamic State has claimed the Las Vegas attack, saying Paddock converted to Islam months ago, but they did not provide evidence. Investigators in Las Vegas also have not found evidence of ties to terrorism.
IS often claims attacks by individuals inspired by its message but with no known links to the group.
Lombardo said there was no evidence of a connection.
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"We are pretty confident that there is no longer a threat," said Sheriff Joseph Lombardo with the Las Vegas Metropolitan Police Department.
Singer Jason Aldean was just finishing up his set at the Route 91 country music festival when a series of shots - about 200 rounds within 4 1/2 minutes - were fired in rapid-fire bursts, witnesses said. About 22,000 people were in attendance.
Terrified concertgoers ran for cover and described a scene of mass chaos as people were felled by bullets and friends tried to help them at the scene.
"It was the craziest stuff I've ever seen in my entire life," 36-year-old Kodiak Yazzie said. "You could hear that the noise was coming from west of us, from Mandalay Bay. You could see a flash, flash, flash, flash."
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Mike Cronk said his friend was shot, and in the chaos, he tried to help others around him.
"We're listening to Jason Aldean sing, and it sounded like some firecrackers going off," Cronk said. "My buddy is like, 'I'm hit.' He was standing right next to me. So he took three shots to the chest."
Cronk said his friend just got out of surgery and was awake and talking. He added that while they were transporting victims in a private truck, they were able to stop an ambulance for help, but it was too late for one of the victims.
"One of the young men that I was carrying actually died in my arms while they were loading up the ambulance," he said.
Aerial footage from the strip shows a window shot out at the Mandalay Bay hotel, appearing to be the room where the gunman opened fire on the crowd below. Investigators were seen inside the room Monday morning.
As news of the shooting spread, rumors of multiple shooters at multiple locations spread through social media. Police later dismissed those reports, saying there was one shooter at one location. There were also no explosives involved, other than those used by the SWAT team to enter the suspect's hotel room, Lombardo said.
In the initial chaos, authorities shut down part of the Las Vegas Strip and the 15 Freeway. A groundstop was initiated for Las Vegas' McCarran International Airport for departing and arriving flights. Flights were allowed to resume less than two hours later, but travelers were advised to check with their airlines as some delays were possible.
Las Vegas-based Allegiant airline said it will help families of victims with free flights to Las Vegas. It will also allow travelers who had been scheduled to fly to Las Vegas to cancel their plans without penalty.
"Las Vegas is Allegiant's hometown and on this tragic day we are heartbroken but gratified to see the world rally around our community with so much support and love," the airline tweeted.
President Donald Trump extended his condolences to the victims and their families, and he condemned the shooting as an "act of pure evil."
"Our unity cannot be shattered by evil, our bonds cannot be broken by violence," the president said. "We call upon the bonds that unite us: our faith, our family, and our shared values. We call upon the bonds of citizenship, the ties of community, and the comfort of our common humanity."
Trump ordered that the American flag at the White House and at all public buildings across the nation be flown at half-staff.
A woman described as a roommate and traveling companion of Paddock, identified as Marilou Danley, was initially sought as a person of interest. After detectives spoke with her, they determined she was not involved with the shooting. She is believed to be out of the country, in Tokyo.
Officials said they continue to seek a vehicle registered to Paddock, described as a Hyundai Tucson with Nevada plate 114-B40. A Chrysler Pacific Touring minivan with Nevada plate 79D401 also connected to him was found.
ABC News and the Associated Press contributed to this report.