"I think people felt about 30 seconds, at the most, of shaking. The shaking and the quakes bounce around the Earth and come up again," said geologist Dr. Phillip Carpenter.
For scientists like Dr. Carpenter, Friday was an exciting day.
"The last time we had an earthquake here we felt was in 2004," Carpenter said.
Dr. Carpenter also said rocks shifting below the Earth's surface can send vibrations hundreds of miles away.
"Things move a little bit. They move up and down or back and forth. When that happens, it sends out shockwaves, which, eventually, we feel as earthquake waves," Dr. Carpenter said.
He also said the underground movement happened along what is called the Wabash Fault.
"They build up slowly along a weak zone. It gets to a point where the weak zone can no longer support the stress, and it snaps. And that's when you get an earthquake," said Carpenter.
Dr. Carpenter said incidents like Friday's earthquake give credence for more research about earthquakes in the Midwest. He said they haven't been studied nearly as much as some of the quakes on the West Coast. But he said incidents like Friday's are important to study and understand how, if there was a big earthquake, it would affect residents in the Chicago area and areas south and north.
"It shook our house where it woke me up," David Behm of Philo, 10 miles south of Champaign, said of the quake. "Windows were rattling, and you could hear it. The house was shaking inches. For people in central Illinois, this is a big deal. It's not like California."
In Mount Carmel, a woman was trapped in her home by a collapsed porch but was quickly freed and wasn't hurt, said Mickie Smith, a dispatcher at the police department. The department took numerous other calls, though none reported anything more serious than objects knocked off walls and out of shelves, she said.
Also in Mount Carmel, a two-story apartment building was evacuated because of loose and falling bricks. Police cordoned off the building, a 1904 school converted to residences.
Bonnie Lucas, a morning co-host at WHO-AM in Des Moines, said she was sitting in her office when she felt her chair move. She grabbed her desk, and then heard the ceiling panels start to creak. The shaking lasted about five seconds, she said.
The early morning quake rattled a large swath of the nation.
"This was widely felt, all the way to Atlanta, a little bit in Michigan," said USGS geophysicist Carrieann Bedwell.
Phones started ringing at the Crawford County Sheriff's Department in Robinson, about 15 miles north of the epicenter, but there were no immediate reports of damage, dispatcher Marsha Craven said.
"They didn't know if it was the refinery blowing up or an earthquake," she said, referring to the a local petroleum refinery.
In Cincinnati, Irvetta McMurtry said she felt the rattling for up to 20 seconds.
"All of a sudden, I was awakened by this rumbling shaking," said McMurtry, 43. "My bed is an older wood frame bed, so the bed started to creak and shake, and it was almost like somebody was taking my mattress and moving it back and forth."
Lucas Griswold, a dispatcher in West Salem, said the Edwards County sheriff's department received reports of minor damage and no injuries.
"Oh, yeah, I felt it. It was interesting," Griswold said. "A lot of shaking."
There were very few reports of damage in West Salem, a small town dotted by brick buildings and ranch-style homes in the middle of farm country.
"We're very thankful we had no one injured," said Harvey Fenton, West Salem's police and fire chief.
Fenton was asleep in his house when the earthquake hit.
"A major shaking is the best way I can describe it," said Fenton, 58, who wasn't sure what to make of the sudden rumbling, thinking it was thunder or perhaps an explosion.
In Louisville, Ky., the quake caused some bricks to fall off a building near downtown. Television video showed them strewn in the street.
The quake shook skyscrapers in downtown Indianapolis, about 160 miles northeast of the epicenter, and in Chicago's Loop, 230 miles north of the epicenter.
Chicago officials were checking structures downtown to ensure there was no damage.
On the Edens Expressway near Chicago, a rebar pushed up from the pavement Friday morning and "flattened a few tires," said Illinois State Police spokesman Lt. Scott Compton, but it was unclear whether the quake had caused the expressway damage.
The strongest earthquake on record with an epicenter in Illinois occurred in 1968, when a 5.3-magnitude temblor was recorded about 75 miles southeast of St. Louis, according the USGS. The damage was minor but widespread and there were no serious injuries.
In 1811 and 1812, the New Madrid fault produced a series of earthquakes estimated at magnitude 7.0 or greater said to be felt as far away as Boston. They were centered in the Missouri town of New Madrid (pronounced MAD rid), 140 miles southeast of St. Louis.
Experts say that with the much higher population in the Midwest, another major quake along the New Madrid fault zone could destroy buildings, bridges, roads and other infrastructure, disrupt communications and isolate areas.
The Associated Press contributed to this report.