Venomous (Poisonous) Snakes in Illinois

Written by Emmanuel Kingsley
Updated: October 31, 2022
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The state of Illinois is no stranger to snakes. Its swamps, ponds, lakes, marshes, forests, lakes, grasslands, and many other parts of the state are known to habit over 40 snake species! This includes a significant number of endangered snakes. According to the Illinois State Government, as of 2020, 11 species, including the great plains rat snake, were listed as endangered.

Luckily, the state doesn’t have nearly as many venomous snakes. Only a tenth of Illinois’ entire species has dangerous venom. Let’s take a look at the venomous snakes in Illinois, but let’s consider an important question first: Are snakes venomous or poisonous?

Are Snakes Venomous or Poisonous?

Snakes are venomous because they inject venom which is solely produced for that purpose. If you find this slightly confusing: here’s a simple way around it.

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  • If a snake bites you and you die, it is venomous.
  • If you bite or eat a snake and die, the snake is poisonous.

The term poisonous is reserved for deadly substances that are ingested (eaten, absorbed, etc.) On the other hand, “venomous” is better suited for situations where the deadly substance is injected through some means (think snake fangs).

All caught up with the right terms? Great! Let’s take a look at the venomous snakes in Illinois.

4 Venomous Snakes in Illinois

The state of Illinois is home to copperheads, cottonmouths, Massasaugas, and timber rattlesnakes. These four are the venomous snakes in Illinois.

Copperheads (Agkistrodon contortrix)

The Copperhead’s scales are keeled, and their eyes have vertical pupils that make them resemble cat’s eyes.
Eastern copperheads are venomous snakes found in the lower Illinois River valley as well as south of Route 16.

©Creeping Things/

Eastern copperheads, also called copperheads, are skilled and deadly pit vipers. They aren’t long snakes and are known to attain a maximum length of 36 inches. However, despite their medium-sized bodies, eastern copperheads are known for their deadly venom. Luckily, their venom is usually only deadly to their prey. In 1967, research scientist Henry M. Parrish published an article explaining that 99.9% of people bitten by copperheads survive.

Despite this low fatality rate, these snakes are still deadly and should be regarded as such. In addition, their bites are extremely painful and are known to redden and swell. Their bites are even known to cause nausea, disturbed vision, and inability to breathe – among other dreadful symptoms.

However, Illinoisans are rather familiar with these snakes as they are commonly found in the lower Illinois River valley as well as south of Route 16. If you’d like to avoid snakes in these parts, stick to cleared routes and avoid wandering off.

Northern Cottonmouth (Agkistrodon Piscivorus)

Northern cottonmouths, commonly found in Jacksonville’s Carbondale, pick habitats close to water.

©Linda Burek/

The cottonmouth is another of Illinois’ venomous snakes. This species is easily identified by its uniform cross band patterns spread across its black or brown body. Also known as water moccasins, they usually measure around 30 to 40 inches long and are known for being aggressive and highly venomous.

In Illinois, cottonmouths are found mostly in Jacksonville’s Carbondale. However, they are best avoided as their bites are venomous enough to kill humans. Cottonmouths aren’t exactly aggressive but are known to stand their ground against intruders. This is probably where their bad reputation comes from. Generally, cottonmouths stay close to water. They are usually found in a wide range of freshwater habitats and are great swimmers.

Timber Rattlesnake (Crotalus horridus)

Timber rattlesnaake coiled in a loop
Timber rattlesnakes are deadly pit vipers found in counties that have forested river bluffs and border the Mississippi River.

©Frode Jacobsen/

Timber rattlesnakes are deadly pit vipers known for their dangerous venom. In the state of Illinois, they are regarded as endangered and venomous, making it illegal to harass, kill, collect, or possess any specimen. This law is in place for a good reason; timber rattlesnakes have venom strong enough to kill a human!

Consequently, only trained experts should handle these snakes. This isn’t to say that they are aggressive- they aren’t. Timber rattlesnakes are known for making a big show of rattling and feinting before striking. 

Timber rattlesnakes are also known to only bite when they feel threatened or scared. If you’re on the lookout for timber rattlesnakes in Illinois, you’ll be pleased to know that they are found in multiple counties. They can be found in counties that have forested river bluffs and border the Mississippi River.

Eastern Massasauga Rattlesnake (Sistrurus catenatus catenatus)

Eastern Massasauga rattlesnakes are venomous snakes found in the northern two-thirds of Illinois.

©Ryan M. Bolton/

Massasaugas are regarded by Illinoisians as a shy, docile, but venomous snake species. Known as one of the least-venomous rattlesnakes, massasauga rattlesnakes have quite a bit of history with humans. This snake species is known never to rattle its tail when it believes humans are near and several researchers believe that this could be because they were very frequently hunted by humans many years ago. It is believed that they do this to avoid drawing any attention to themselves.

Despite its placement on the “least venomous list,” massasauga rattlesnakes are known to have very painful bites. They can also be significantly venomous and should be treated urgently. Eastern massasauga rattlesnakes can be found in the northern two-thirds of Illinois. 

What to Do If You Spot a Venomous Snake in Illinois

If you spot a venomous snake in the state of Illinois, do not harm it. Remember that several species of Illinois snakes are protected, making it illegal to capture, kill, or trade them. Snakes are an important part of the ecosystem, so if you spot one in its natural habitat, respect its space and exit calmly.

Remember that you do not want to scare or agitate them in any way. Most snakes are happy to leave you alone if you do too. If you spot the snake in your home, ensure that everyone, including pets, exits safely. If the snake is acting erratic, place an emergency call as soon as possible. However, if it is mild-mannered, get everyone to safety and reach out to Illinois pest control services.

What to Do If You Get Bitten by A Poisonous (Venomous) Snake in Illinois

Although snake bites in Illinois are a rarity, they still occur. If you’ve been bitten by a venomous snake in Illinois, follow the following steps:

  • Remain calm and get as far away from the snake as possible. Snakes are known to bite multiple times.
  • Treat snake bites as an emergency and contact emergency services. It would help if you can identify what type of snake bit you, but if you don’t, don’t sweat it. Doctors are amazing at what they do.
  • Remember to stay calm and sit as still as possible. Moving around could help the venom circulate even faster. Also, do not attempt to suck out the venom or cut off the bitten part. Self-administered treatments like these only worsen the situation that could be otherwise rectified with anti-venom.

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Rattlesnakes While HIking - Timber Rattlesnake
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FAQs (Frequently Asked Questions) 

How many rattlesnakes live in Illinois?

There are two rattlesnake species in Illinois, the eastern massasauga and the timber rattlesnake. Both rattlesnakes only live in southern Illinois.

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