When the clowns began to surface, many guessed they might be part of a guerrilla marketing campaign for a horror movie.
Now, after a summer of sightings, several clown-related threats, robberies and close encounters involving children have law enforcement and communities across the country on edge.
Some of the first clown sightings began back in June and August, stretching from the Midwest to the East Coast and through the south. In Wisconsin, Gags the Green Bay Clown gained viral status after grainy photos of a clown surfaced walking the streets under the cover of night.
Speculation was that Gags and other clown sightings might be related to a viral marketing campaign for a movie, haunted house or other entertainment product or venue.
The clown sightings took a scary turn in late August, when authorities in South Carolina began reports of a person dressed as a clown trying to lure children into the woods.
Deputies said they received several reports of suspicious characters dressed like clowns with white face paint who were flashing green lasers and enticing kids with large amounts of money.
In mid-September, three children in Georgia told police about an incident involving two adult men dressed as clowns.
McDuffie County deputies say Cameron Frails, 12, and his little brother were walking to a bus stop after 6am when they were chased by men donning all black clothing, clown masks and red wigs.
The neighbor girl, Hannah Rice, saw the clowns following the boys out from between two mobile homes before the chase, deputies said.
A week later, police in Pottsville, Pennsylvania began investigating a frightening claim by a 12-year-old who said she was chased by a clown through a park.
Brianne Hawke, 12, told WNEP-TV that a little boy came screaming through the park after allegedly seeing a group of clowns "eating something in the woods."
"A clown started chasing us up here and turned around and went back to the woods," she said. But the terror wasn't over.
The alleged clowns returned, she said, throwing sticks at the children before hurling curse words at them. "It was scary," Brianne says.
After alleged clown sightings in South Carolina, southern Kentucky, Tennessee and a few other states, the Tennessee Highway Patrol issued a warning to parents to watch the kids and to be on the lookout for anything out of the ordinary.
The threat, they said, was the possibility of predators in clown costumes seeking to lure children into the woods.
Around the same time, law enforcement said a teenager in Coffee County, Tennessee claimed to have been attacked by a clown.
All the while, retail shops across the U.S. began rolling out Halloween costumes including an assortment of clown-related costumes, wigs, makeup and accessories.
Arizona officials blame an abnormal number of school absences on a social media threat featuring a clown image.
Between two Phoenix school districts, 24 schools were named in a multitude of threats posted online. Parents and students were shaken, with about half of the 3,000 students at Marydale High School skipping class out of concern.
Three juveniles were arrested after the FBI joined the investigation. They face felony charges, but law enforcement said they believed others may be involved.
Later in the week, schools in Ohio and Tennessee would be targeted by similar clown-related threats.
The next day in Phoenix, police say two different fast food restaurants were robbed by suspects wearing clown masks.
Around 8pm Tuesday, a Taco Bell restaurant was allegedly hit by an armed robber. As police were busy investigating, the suspects allegedly hit a Domino's restaurant nearby.
Two 17-year-olds were arrested in connection with the robberies.
Several 911 calls in Long Island, New York were recorded in regards to clown incidents.
In one call, drivers reported a group of clowns were jumping in front of moving vehicles in Brentwood.
No one was arrested after the incidents.
The next day in Tennessee, police say a clown armed with explosives walked into a bank and demanded money from a teller.
Memphis police said one person clad with a clown costume and another person got away with an undisclosed amount of cash.
The following Monday, Philadelphia police identified a 13-year-old girl as the person who made so-called "clown threats" toward local schools.
Investigators said the girl told them it was a "prank" committed with a friend at her school and she never had any intent to harm anyone.
A day later, Hammond police said they were investigating social media threats made by clowns against several northwest Indiana schools.
"So far there have been no reports of confirmed clown sightings in the City of Hammond and at this time the information appears to be solely based on Facebook," Hammond Police Lt. Richard Hoyda said.
The following day, a teenager was arrested in connection with a fake clown threat in Hammond, Ind., just as worried parents accompanied their children to school because of creepy clown threats in the Chicago area.
Chicago Public Schools said it was investigating approximately 50 social media incidents with threats involving clowns.
Authorities across a dozen suburbs said they were also investigating various clown-related threats and sightings.
The next day, a mother in California said she had to fight off a man dressed in a clown suit to keep him from snatching her 1-year-old daughter out of her arms.
She said he wore a blue curly wig, but no mask or makeup on his face. After a brief conversation, she said he grabbed for her daughter's arm.
That same day, a 13-year-old girl was charged in an alleged murder-for-hire plot involving a clown and her teacher.
Authorities said the girl asked a person posing as a clown on social media to kill her teacher.
The girl was charged with one count of threatening to kill by electronic message.
Two parents were arrested on charges they left their 4-year-old child at home so they could allegedly terrorize a neighborhood while dressed as clowns.
Police in Menasha said several people wearing clown costumes were seen chasing cars in the early morning hours of Oct. 7.
Over the weekend, someone in a clown costume was caught on video hanging off the back of a moving bus in Detroit.
WDIV reports the video has more than 500,000 views on social media. The person who shot the video said it was filmed on Saturday.
The Detroit Department of Transportation said it was increasing security following the incident.
McDonald's Corp. said it is being "thoughtful in respect to Ronald McDonald's participation in community events" as a result of the "current climate around clown sightings in communities."
The burger chain's decision comes after a rash of pranks around the country that have involved eerie clown sightings.
A person dressed as a clown was apparently scared off after the man he was approaching fired a gun into the air, according to the Los Angeles County Sheriff's Department.
Authorities said a man called 911 to report that someone dressed in a clown costume holding a knife approached his home. The man told deputies he fired a warning shot into the air and the suspect ran from the area.
Just a few weeks before Halloween, Target said it is removing clown masks from store shelves and its website after scary clown threats have been reported across the country.
"We had a few masks in stores, which we began to pull last week," a media representative of Target told ABC News. "We also have edited down our assortment online. You'll still find clown masks there, but we made the decision to pull back on the number."
A Mississippi county has had enough of the creepy clown craze, at least until after Halloween.
Kemper County supervisors enacted a clown ban this week, temporarily preventing people from dressing as clowns. Anyone caught in public wearing a clown costume, mask or makeup could face a $150 fine.