Discover The 10 Largest Animals in Illinois, and Where You’ll Find Them

Written by Hannah Ward
Updated: October 8, 2022
© Cooper
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Also known as the Prairie State, Illinois is famous for its vast open prairies and grasslands. It also has an important network of rivers and lakes – being one of the states which encompasses the Great Lakes and with much of its western edge being bordered by the Mississippi River. Illinois is also home to a diverse range of animals – including the white-tailed deer, which is the state animal. But that’s not all there is to offer, so join us as we discover some of the largest animals in Illinois and where you’ll find them!

1. Timber Rattlesnake

Timber Rattlesnake coiled on a rock
Timber Rattlesnakes are one of the most venomous snake in the U.S.


There are four venomous snakes in Illinois and the largest is the timber rattlesnake, which reaches 3 to 5 feet long. Timber rattlesnakes are yellowish brown and have distinctive dark brown or black crossband markings, which often have irregular zigzag edges. These snakes are highly venomous, but luckily this is somewhat counteracted by their relatively calm manner and long winter brumation period. Timber rattlesnakes are most often found in thick forest regions with the exception of pregnant females, which prefer rocky areas where they can bask in the sun. In Illinois, timber rattlesnakes are found in the southernmost regions of the state in forest regions near the Mississippi River.

2. Giant Stag Beetle

Giant Stag Beetle on a tree branch.
Giant Stag Beetles (Lucanus elaphus) depend on wood that is dead or dying.


The largest beetle in Illinois is the giant stag beetle, which reaches between 1.5 and 2.5 inches long. Giant stag beetles have sturdy black bodies with formidable mandibles. Males have larger mandibles than females and often use them to fight with other males for mating rights with the females. Giant stag beetles are typically found in old woodlands where there are plenty of dead or decaying trees. This is because their larvae feed on rotting wood, although as adults they eat little to no food at all.

3. Blue Catfish

Blue Catfish
Blue Catfish eat a large variety of fish and other water animals.

©M Huston/

Another large animal in Illinois is the blue catfish, which is a large predatory fish that can inhabit both fresh and brackish water. They are a blueish grey color and have thick, heavy bodies with two distinctive barbels on their lower jaw. Blue catfish primarily live in and around the Mississippi River and can attain lengths of more than 6 feet and weights up to 150 pounds. The largest blue catfish in Illinois was caught in the Mississippi River in 2005 and weighed a massive 124 pounds and 4 ounces. Blue catfish eat a wide range of fish, crawfish, crabs, frogs, and mussels, and in some places they are classed as pests due to their voracious appetite.

4. Sandhill Crane

sandhill crane migration
Sandhill Cranes are among the most common and populous cranes.

©Tom Zeman/

The tallest bird in Illinois is the sandhill crane, which stands 2 feet, 7 inches to 4 feet, 6 inches high and has a wingspan of 6 feet, 6 inches. Sandhill cranes are typically grey with red foreheads and a long, dark colored bill. They have a distinctive appearance when flying, as their neck sticks straight out and their legs trail behind them. Sandhill cranes have a loud, trumpeting call that can be heard from several miles away. They live in freshwater habitats such as swamps, marshes, and river basins. They are omnivores and eat a mixture of plant material, small mammals, reptiles, and frogs. Sandhill cranes are widespread across Illinois but some of the best places to see them are in McHenry and Lake counties.

5. White-Tailed Deer

A white-tailed deer doe and its two fawns in an open meadow in summer.
A white-tailed deer doe and its two fawns in an open meadow in summer.

©Tony Campbell/

One of the largest animals in Illinois is the white-tailed deer, which is also the only species of deer native to the state. White-tailed deer are a reddish brown color in the summer and a greyish-brown color in the winter. They are best known for the distinctive white patch on the underside of their tail, which is easiest to see when they raise their tail in alarm when disturbed. Male white-tailed deer are larger than the females and the heaviest can reach 400 pounds with the shoulder height usually being anything up to 4 feet high. White-tailed deer are capable of living in a wide variety of habitats, including forests, grasslands, and prairies. However, in Illinois they are often found in woodland areas near the major rivers which run through the state – the Mississippi, Illinois, and Kaskaskia rivers.

6. Cecropia Moth

A cecropia moth is sitting on a huge maple leaf. The Cecropia moth is the largest and heaviest moth in North America.
A cecropia moth sitting on a huge maple leaf. The Cecropia moth is the largest and heaviest moth in North America.

©Cathy Keifer/

The largest insect in Illinois is the cecropia moth, which is also the largest moth in North America. Cecropia moths have a massive wingspan of around 7 inches and have a stunning appearance with red, white, and tan bands on their dark brown or black wings. Cecropia moths are silk moths and don’t have a digestive system or a functional mouthpart. This means that they actually only survive for approximately two weeks in their adult form. Cecropia moths often live in hardwood forests and are found all across Illinois.

7. Bald Eagle

baby bald eagle with mother
The bald eagle is one of the largest birds in North America.

©Jon C. Beverly/

The largest bird in Illinois is the stunning bald eagle, which is easily recognized by its dark brown plumage and distinctive white head and tail. Bald eagles have a massive wingspan that ranges between 5 feet, 11 inches and 7 feet, 7 inches. They are also well known for their ability to create huge nests in trees. The largest nests can be as much as 9 feet wide and 20 feet deep. They get this big because these birds simply add extra material to it each year so that it gradually builds up over time. Bald eagles are sea eagles and their diet mainly costs of fish. They typically live near large bodies of water such as lakes and coastlines. Bald eagles frequent Illinois in the winter and they can be found all over the state in suitable habitats.

8. Lake Sturgeon

two lake sturgeons
Lake sturgeon are considered an endangered species in Illinois.


One of the largest animals in Illinois and the largest fish in the state is easily the lake sturgeon. The largest caught in Illinois was 7 feet, 11 inches long and weighed an incredible 310 pounds. It was caught in Lake Michigan in 1943 and is one of the biggest lake sturgeon ever recorded. Lake sturgeon are freshwater fish and have an elongated spade-like snout. They are predominantly bottom feeders and use their snout to search for insects, snails, clams, and crayfish. Lake sturgeon live in large lakes and rivers – particularly around the Great Lakes and the Mississippi River. They are an endangered species, and all lake sturgeons caught in Illinois must be returned to the water. In Illinois they are most often found in Lake Michigan.

9. Gopher Snake

gopher snake
The gopher snake is commonly misidentified as a rattlesnake because of its markings and defensive behavior. It may hiss loudly, flatten its head, vibrate the tail, and strike when annoyed.

©Tim Pleasant/

The longest snake in Illinois in the gopher snake, which can reach 9 feet long. Gopher snakes are not venomous and instead kill their prey by constriction and eat a range of rodents and birds as well as pocket gophers. They are typically a yellowish brown color with dark brown spots and blotches down their body. However, there are currently six recognized subspecies of gopher snakes, so there can sometimes be some variation between them. Gopher snakes are often mistaken for prairie rattlesnakes because of their behavior. This is because they tend to rear up off the ground and puff themselves up like a rattlesnake while vibrating their tails. Gopher snakes live in a wide variety of habitats. However, in Illinois they are mainly found in prairies across the central and northern regions of the state.

10. Bison

Herd of bison in river.
Bison were once hunted to extinction in Illinois, but were reintroduced and are now one of the largest animals in the state.

©MONGO – Public Domain

The largest animal in Illinois is the mighty bison. These huge animals stand around 6 feet, 7 inches at the shoulder and can weigh up to 3,000 pounds. Bison are grazers and prefer to live in open and semi-open grasslands and prairies. They typically live in large herds, although the females and calves live in one herd with the males together in smaller “bachelor herds”. Bison were hunted to extinction in Illinois in the early 1800’s, but have since been successfully reintroduced to the state. Today, some of the best places to see them roaming wild are the Midewin National Tallgrass Prairie and Nachusa Grasslands.

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While bison have poor eyesight, they have excellent senses of smell and hearing. Cows and calves communicate using pig-like grunts, and during mating season, bulls can be heard bellowing
© Cooper

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About the Author

I have been writing professionally for several years with a focus on animals and wildlife. I love spending time in the outdoors and when not writing I can be found on the farm surrounded by horses, dogs, sheep, and pigs.

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  1. Land Big Fish Fishing Tackle Marketplace, Available here:
  2. The National Wildlife Federation, Available here:
  3. Insect Identification for the Casual Observer, Available here: