Tick season in Illinois runs from March through November, with peak activity from April through July. Warmer winters have been pushing that window earlier, with ticks emerging as soon as February in some years and staying active into December. If you spend time outdoors in Illinois, from spring mushroom hunting through fall deer season, ticks are a real concern.
When Ticks Are Most Active
The core tick season stretches across nine months, but the highest risk falls in a narrower band. April through July is when adult ticks and nymphs (the younger, poppy-seed-sized stage) are most aggressively seeking hosts. Nymphs are particularly dangerous because they’re tiny enough to go unnoticed on your skin for hours or even days.
Late summer brings its own risk. Tick larvae hit their annual peak from late July through September. Larvae are less likely to carry disease since they haven’t yet fed on an infected animal, but they’re not harmless, and a heavy larval population means more disease-carrying nymphs the following spring. By October and November, activity tapers off, though adult blacklegged ticks can remain active on mild days well into late fall.
Tick Species You’ll Encounter
At least 15 tick species live in Illinois, but only a handful regularly bite people. The ones worth knowing about are the American dog tick, the lone star tick, the blacklegged tick (also called the deer tick), and the brown dog tick.
The American dog tick is the most commonly encountered species statewide. It’s the large, flat tick you’re most likely to find crawling on your clothes or embedded in your skin after a hike. It can transmit Rocky Mountain spotted fever, though cases in Illinois are uncommon.
The lone star tick is primarily found in the southern half of the state, though it occasionally turns up farther north. Females are easy to identify by the single white spot on their back. This species is aggressive, actively pursuing hosts rather than waiting on vegetation. Beyond transmitting ehrlichiosis, lone star ticks are linked to alpha-gal syndrome, a delayed allergic reaction to red meat that can develop after a bite. Symptoms like hives, stomach pain, nausea, or swelling typically appear two to six hours after eating beef, pork, or lamb. Repeated bites seem to raise the risk further.
The blacklegged (deer) tick is the primary carrier of Lyme disease. It’s been found sporadically across many Illinois counties but is most common in northern parts of the state. Winnebago County, in the far north, has some of the highest infection rates: 71% of ticks collected there tested positive for the Lyme bacterium. Statewide, about 43% of collected blacklegged ticks carry the pathogen. Illinois is still classified by the CDC as a low-incidence state for Lyme disease, which can give people a false sense of safety.
The brown dog tick is tropical in origin and can’t survive Illinois winters outdoors. It shows up in homes and kennels, feeding almost exclusively on dogs. It rarely bites people.
A New Arrival: The Asian Longhorned Tick
In April 2024, Illinois became the 20th state to confirm the presence of the Asian longhorned tick, an invasive species first detected in the U.S. in 2017. Three specimens were found in Morgan County during routine surveillance. This tick can reproduce without mating, which means populations can explode quickly. In other countries it transmits several serious diseases, though the risk to people in the U.S. is still being evaluated. Its arrival is another reason to take tick prevention seriously even in central Illinois.
How Lyme Disease Spreads
A blacklegged tick doesn’t transmit Lyme disease the moment it bites. The bacterium that causes Lyme lives in the tick’s gut and needs time to migrate to its salivary glands before it can enter your bloodstream. That process takes at least 24 hours of attachment, and most experts put the window at 36 to 48 hours. This means finding and removing a tick promptly, ideally within the first day, dramatically reduces your risk of infection. Daily tick checks after outdoor activity are one of the most effective things you can do.
How to Remove a Tick Safely
If you find an attached tick, grab fine-tipped, pointy tweezers and rubbing alcohol. Clean the skin around the tick first. Position the tweezers as close to the skin surface as possible, gripping the tick near its head. Pull straight up with slow, steady pressure. Don’t twist or jerk, which can break off the mouthparts. If the head does break off, try to remove it with tweezers, but don’t panic if you can’t. Your skin will push the remnants out on its own as it heals.
No tweezers? You can carefully use your fingers, trying not to squeeze the tick’s body, or loop a piece of thread or dental floss around its jaws and pull straight up. After removal, clean the bite site and your hands with rubbing alcohol or soap and water.
Watch the bite area over the following weeks. Contact a doctor if you develop a fever, chills, headache, muscle aches, or a rash, particularly the expanding circular rash associated with Lyme disease.
Preventing Tick Bites
Tick prevention works on two layers: what you put on your skin and what you put on your clothes.
For exposed skin, repellents containing DEET, picaridin, IR3535, or oil of lemon eucalyptus all work. A concentration of 10% to 25% DEET is adequate for most situations. Going above 50% doesn’t extend protection time. Apply repellent only to exposed skin, never under clothing. If you’re also wearing sunscreen, apply the sunscreen first, wait a few minutes, then add repellent on top. Avoid spraying it directly on your face. Instead, spray your hands and rub it on. Wash treated skin with soap and water once you’re back inside.
For clothing and gear, permethrin is the gold standard. A 0.5% permethrin spray bonds to fabric and lasts through five to seven washes. Apply it outdoors, let treated clothing dry completely before wearing it, and never apply permethrin directly to skin. One important safety note: wet permethrin is toxic to cats, so keep treated items away from them until fully dry.
Beyond repellents, simple habits make a big difference during tick season. Stick to the center of trails. Wear long pants tucked into socks when walking through tall grass or brush. Toss your clothes in the dryer on high heat for 10 minutes after coming inside, since the heat kills ticks that regular washing won’t. And do a thorough full-body tick check, paying special attention to your scalp, behind your ears, under your arms, and around your waistband. These are the warm, hidden spots ticks prefer.