The Biggest Impact Crater in Illinois Is a 5.5 Mile Behemoth

Written by Drew Wood
Updated: August 23, 2023
Share on:


If you travel frequently, chances are at some point, you were routed through the Chicago O’Hare International Airport. O’Hare offers non-stop flights to 214 destinations on every continent and is considered the most-connected international airport in the world. If you had an overnight layover in Chicago, you may have stayed in a hotel in Des Plaines, a suburb just four miles north of O’Hare and home to the biggest impact crater in Illinois.

Talking to your Uber driver, you might have discovered some facts about Des Plaines. For example, it was the birthplace of the first McDonald’s in 1955. Mr. Uber may have told you that the Rivers Casino is a popular venue. He may have shared that downtown Chicago is only 20 miles away. But what your driver probably didn’t know is that the land Des Plaines was built on was once blown sky-high. The strength of this explosion was equivalent to a nuclear weapon many times larger than anything around today. It left behind the biggest impact crater in Illinois — 5.5 miles wide — yet today, few people even know it exists! What caused it? And could it happen again?

Chicago O'Hare International Airport electric neon tunnel

Few travelers navigating O’Hare International Airport realize that an apocalyptic explosion once took place just a few miles from there.


Key Points

  • The biggest impact crater in Illinois is in Des Plaines, a Chicago suburb of 60,000 people located northwest of the city center and north of O’Hare International Airport.
  • The crater is 5.5 miles in diameter. It was made by a meteor or cometary nucleus approximately 200 feet in diameter and perhaps traveling at 30,000 mph.
  • The explosion that created the crater would have been about 20 megatons, vastly larger than the largest nuclear weapons deployed today by the United States.
  • If the same thing happened today, it would blast out windows in downtown Chicago and cause 3rd degree burns on people up to 25 miles away.
  • The impact may have happened as far back as the Permian Period, 280 million years ago. This was long before the dinosaurs appeared on Earth.
  • The crater is now buried under up to 200 feet of earth but can be detected by geological surveys of the shattered rock layers under the surface.
  • Although meteors of this size hit the Earth about once every 2,000 years, they are most likely to hit unpopulated parts of the planet.
  • The odds of being killed by a meteor are much lower than other ordinary hazards we face every day.
flying smoky meteor on background of sky

Most meteors burn up in the Earth’s atmosphere without ever hitting the ground. They’re colloquially called “fireballs” or “shooting stars.”


The Worst Day Illinois Ever Had

On a day perhaps as far back as 280 million years ago, a meteor or cometary nucleus slammed into what is today Des Plaines. It may have been 200 feet or so in diameter, about the length of a semi-truck trailer or the height of a 20-story building. Big, but doesn’t seem that big, right? Well, traveling at perhaps 30,000 mph, it would have exploded with as much energy as a 20-megaton nuclear bomb and created the biggest impact crater in Illinois, 5.5 miles in diameter.

If the same event happened today, it would make a fireball 2.5 miles in diameter. The airport would be heavily damaged, windows in downtown Chicago would be shattered, and people from Waukegan in the North to Naperville in the South would receive 3rd-degree burns. Anyone or anything within 24 miles could be immediately injured by fire or falling debris, including molten rocks thrown out by the explosion. You can use this site to model the scale of a nuclear explosion.

Nuclear Explosion

The explosion that created the biggest impact crater in Illinois was about 20 megatons. The largest nuclear weapons are about 1.2 megatons.

©Romolo Tavani/

What Lived in Illinois at That Time?

What living things might have witnessed the explosion and perished in it? This would have been in the Permian Period. Illinois was part of the Pangaea supercontinent and was above sea level, so it didn’t get a layer of marine fossils from this time as other parts of the continent did. But in the seas, there was a huge variety of marine life, maybe even more species than we have today. Erosion wore down most of the Permian rock layer in northern Illinois, so geologists and paleontologists are not certain what kinds of flora and fauna lived here. The climate was getting warmer throughout this time period, and new species were emerging.

Judging from remains found in other parts of the country, it’s possible Illinois was covered in ferns, mosses, scale trees, early conifers, and ginkgoes. Large salamanders and the primitive ancestors of snakes, lizards, and other reptiles may have lived there. The apex predator of that period in the American South and Southwest was the dimetrodon, a prehistoric reptile with a large sail on its back for balance and thermal regulation. This creature had features that led researchers to think it was an ancestor of mammals. It was still too early for dinosaurs at this time; they wouldn’t appear for tens of millions of years. And the Permian period ended with a mass extinction event that’s still not entirely understood.

Dimetrodon Angelensis

The Dimetrodon was the apex predator of the Permian Period in North America.


Where Can You See the Des Plaines Crater?

Well, actually, you can’t. In the millions of years that have passed since the crater was originally made, the geology of Northern Illinois has changed a lot. A lot of these changes occurred when the entire region was buried under ice in the last ice age. Glaciers buried it under tons of sediment and debris. Now it lies 75-200 feet beneath the eastern part of the city.

So how do we know it’s even there? Because drilling in the 25 square mile area of the 5.5-mile crater, the bedrock was shattered by an impact. The area is riddled with faults and deformations. Large blocks of sediment have been broken and upended from their normal position. The land has been displaced vertically by as much as 600 feet in some areas. Shatter cones which only occur under the huge pressures of a meteorite impact have also been discovered beneath the site. So, researchers today have a high degree of confidence that a meteor strike happened at this site. The evidence remains hidden deep under today’s peaceful city of Des Plaines.

Aerial View of the Chicago Suburb of Des Plaines in Autumn

The biggest meteor crater in Illinois lies deep beneath the surface of Des Plaines, a Greater Chicago suburb of 60,000 people.

©Jacob Boomsma/

Where Is the Des Plaines Impact Crater Located on a Map?

Des Plaines is a city located in Cook County, Illinois. It is situated approximately 17 miles northwest of downtown Chicago and covers an area of 14.42 square miles.

If you are looking for directions to Des Plaines, there are several ways to get there, depending on your starting point. One option would be to take I-90 West from Chicago and exit onto Northwest Highway towards Des Plaines. Another option would be to take the Metra Union Pacific/Northwest line, which stops at the Des Plaines station located in the heart of downtown Des Plaines. Whether you’re driving or taking public transportation, it’s easy to find your way to this vibrant suburban community with plenty of attractions and amenities for visitors and residents alike!

How Likely Is It to Happen Again?

About once every 2,000 years, a meteor the size of a football field (360 feet) hits the earth. Fortunately, 70% of the Earth is covered in water, so that’s the most likely place for impact. And of the land surface, 50% is relatively untouched by people: the Antarctic, deserts, high mountains, and deep forests. So altogether, there’s an 85% chance that an asteroid striking the earth will hit someplace where there are no people.

The odds of dying in a meteor strike have been calculated at 1 in 250,000. So, it’s less likely than dying in a plane crash (1 in 30,000). However, it’s more likely than winning the PowerBall lottery (1 in 195,000,000). You can just imagine how infinitely small the chances are of it happening in the same place twice. So, if you’re afraid of asteroids, maybe you’ll decide Des Plaines is one of the safest places to live!

The photo featured at the top of this post is © Romolo Tavani/

Share on:
About the Author

Drew Wood is a writer at A-Z Animals focusing on mammals, geography, and world cultures. Drew has worked in research and writing for over 20 years and holds a Masters in Foreign Affairs (1992) and a Doctorate in Religion (2009). A resident of Nebraska, Drew enjoys Brazilian jiu-jitsu, movies, and being an emotional support human to four dogs.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.