For decades, Lyme disease was understood by most Americans as an East Coast and Upper Midwest problem, something that happened in the forests of Connecticut, New York, Wisconsin, and Minnesota. That understanding is now outdated in a significant portion of the country.
Blacklegged ticks — the species that transmits Lyme disease — have expanded across Indiana, Illinois, and Ohio and are now being found in suburban parks, neighborhood green spaces, and backyards in major metro areas where residents and physicians alike may not yet be thinking about Lyme disease as a local risk.
The 2026 Companion Animal Parasite Council forecast projects that some of the greatest expansions in Lyme disease risk will occur in Ohio, Kentucky, West Virginia, Indiana, Illinois, North Carolina, and Michigan — states that until recently saw very few cases. Those numbers matter because CAPC notes that areas of higher canine Lyme risk consistently mirror areas where people contract Lyme disease, making dog testing data one of the most reliable early indicators of human risk.
And researchers speaking at the Johns Hopkins Bloomberg School of Public Health media briefing in May 2026 said the spread is accelerating — driven by climate change, expanding deer populations, and suburban development patterns that bring humans and wildlife into closer contact than at any point in recorded history.
Why This Matters
The consequences of Lyme disease expanding into new urban and suburban areas are not only epidemiological. They are diagnostic. In states and cities that have long been outside the traditional Lyme disease endemic zone, clinicians are less likely to order Lyme disease testing for patients with compatible symptoms — because they have been trained to think of it as something that happens elsewhere.
In the suburban Chicago area, around half of the adult blacklegged ticks now test positive for the bacteria that causes Lyme disease — which was never the case before, said Johnny Uelmen, a disease ecologist and researcher at the University of Wisconsin School of Medicine and Public Health.
That is not a rural statistic. Chicago is the third-largest city in the United States. Its suburbs — including communities in Cook, DuPage, Kane, Lake, and Will counties — are densely populated areas where millions of people walk dogs in forest preserves, let children play in backyards, and bike through paths that border wooded areas. If half of adult blacklegged ticks in those areas carry Lyme disease bacteria, the risk is no longer theoretical.
What We Know So Far
The geographic expansion of blacklegged ticks is documented across multiple independent data sources, not just a single report.
In Ohio: A 2026 study from Ohio State University found that the risk of encountering Lyme disease in Ohio is now comparable to historically high-risk states like Connecticut. Blacklegged ticks have now been reported in all 88 Ohio counties. Some areas of eastern and southern Ohio show infection rates approaching 40 to 50 percent of ticks tested carrying the Borrelia burgdorferi bacteria that causes Lyme disease. The CAPC 2026 forecast identifies eastern Ohio as one of the fastest-growing risk areas in the country.
In Indiana: Blacklegged ticks have now been found in almost every county across Indiana, according to Purdue University's Medical Entomology program. The tick was first documented in northwestern Indiana in 1987 and has expanded progressively across the state since then. Of the 339,364 dogs tested in Indiana in 2025, 15,551 tested positive for Lyme disease — a rate of approximately 1 in 20 dogs, according to Indiana Lyme Connect.
In Illinois: Around half of adult blacklegged ticks in the suburban Chicago area now test positive for Lyme disease-causing bacteria, according to Uelmen. The lone star tick, established in southern Illinois and Indiana, is also traveling northward, expanding the range of a second tick species with disease-carrying potential.
Where the Risk Is Greatest in the Midwest
Dr. Thomas Hart, an infectious disease microbiologist at the Johns Hopkins Bloomberg School of Public Health's Lyme and Tick-Borne Diseases Research and Education Institute, explained the environmental drivers at the May 2026 briefing: climate change is producing shorter and milder winters, which allow more ticks to survive into the following year. Expanding deer populations — which serve as reproductive hosts for adult blacklegged ticks — are present in suburban areas at historically high densities. And suburban development patterns are placing human housing in closer contact with the wooded and brushy edges where ticks live.
Specific cities and areas facing elevated risk in these three states include:
- In Ohio: Columbus, Cleveland, Cincinnati, Dayton, and their surrounding suburban and exurban counties, with eastern and southern Ohio counties showing the highest current infection rates
- In Indiana: Indianapolis, Fort Wayne, Bloomington, and communities across nearly all 92 counties
- In Illinois: Chicago's Cook County and all adjacent suburban counties — DuPage, Kane, Lake, Will, and McHenry — as well as central and southern Illinois
The risk is not limited to parks, forests, or rural areas. Blacklegged ticks live in the transitional zones where grass meets brush, along fence lines, in leaf piles, and in landscaped yards that border natural vegetation. In areas where deer regularly move through suburban neighborhoods — which includes most of metropolitan Ohio, Indiana, and Illinois — ticks can be found in ordinary backyards.
What Doctors and Experts Say
Dr. Thomas Hart of the Johns Hopkins Bloomberg School of Public Health's Lyme and Tick-Borne Diseases Research and Education Institute said at the May 2026 briefing that the increase in tick populations is being caused primarily by climate change and the resulting effects on tick survival, deer populations, and the geographic range of suitable tick habitat.
Johnny Uelmen, disease ecologist at the University of Wisconsin School of Medicine and Public Health, said that warmer winters brought on by climate change are creating a friendlier environment for ticks in the Midwest and that expanding deer populations are likely to play a role in the spread of both blacklegged ticks and lone star ticks.
Nicole Baumgarth, DVM, PhD, director of the Lyme and Tickborne Diseases Research and Education Institute at Johns Hopkins Bloomberg School of Public Health, noted at the same briefing that the 2026 ER visit data represent only the tip of an iceberg — the vast majority of tick exposures, and a significant portion of resulting Lyme disease infections, never reach an emergency room and may not even reach a physician at all.
What the Evidence Shows and What It Does Not
MedicalDaily Evidence Check
- Data sources: 2026 Companion Animal Parasite Council annual forecast; Ohio State University 2026 Lyme disease risk study; Purdue University Medical Entomology program data; Johns Hopkins Bloomberg School of Public Health Media Briefing, May 5, 2026; University of Wisconsin tick research (GV Wire, July 10, 2026)
- What the evidence shows: Confirmed geographic expansion of blacklegged ticks into all 88 Ohio counties, nearly all Indiana counties, and suburban Chicago-area counties; infection rates in ticks in some areas approaching 40-50%; canine Lyme disease positive test rates in Indiana at approximately 1 in 20 dogs tested
- What the evidence does not prove: Final 2026 human case counts for Ohio, Indiana, or Illinois have not been released; tick infection rates and human case rates are not directly interchangeable
- What readers should know: The risk is real, growing, and no longer confined to wooded rural areas. Prevention is effective and inexpensive.
Who Faces the Greatest Risk in These States?
Midwest residents most at risk for Lyme disease exposure in 2026 include:
- People who walk dogs in forest preserves, parks, or natural areas in the Chicago metro, Columbus, Indianapolis, Cincinnati, Cleveland, Fort Wayne, or Dayton
- Children who play in leafy or brushy outdoor areas
- Homeowners whose yards border natural vegetation, particularly in suburban and exurban areas
- Outdoor workers in landscaping, construction, or groundskeeping in affected counties
- People who hike, mountain bike, or use any trail that passes through or alongside wooded areas
- Pet owners — dogs bring ticks into the home, exposing family members who never go near wooded areas
- People who have never been told by their doctor to consider Lyme disease as a local risk and therefore may not report a tick bite or request testing
Symptoms and Warning Signs to Watch For
Not all Lyme disease infections produce the classic expanding bull's-eye rash. Studies suggest the rash — erythema migrans — does not appear in a significant minority of cases. Its absence does not rule out infection.
Early Lyme disease, appearing days to weeks after a bite, may include a round or expanding rash with or without a central clearing, fever, fatigue, chills, headache, muscle and joint aches, and swollen lymph nodes.
Later-stage Lyme disease, appearing weeks to months after untreated early infection, can cause severe joint pain — especially in the knee — facial drooping or Bell's palsy, heart rhythm irregularities, nerve pain in the hands or feet, and in some cases inflammation of the brain or spinal cord.
If you live in Indiana, Illinois, or Ohio and develop any of these symptoms after potential outdoor exposure — particularly after a tick bite — tell your doctor specifically that you are concerned about Lyme disease and request testing. Do not assume your doctor will think of it without being told. Ordering the right test requires the right clinical index of suspicion.
What You Can Do Now
- Treat Lyme disease as a local risk in Indiana, Illinois, and Ohio — because it is. Adjust your prevention practices accordingly, year-round.
- Apply an EPA-registered insect repellent containing DEET, picaridin, or IR3535 before any outdoor activity in grassy, brushy, or wooded areas. Find options at the EPA's insect repellent finder .
- Apply permethrin to clothing, shoes, and outdoor gear — or purchase pre-treated clothing.
- Perform a full-body tick check after any time outdoors, including time in suburban parks or your own backyard if it borders natural vegetation.
- Check your pets daily for ticks. Talk to your veterinarian about tick prevention for your dog — CAPC recommends year-round tick prevention for dogs in expanding-risk areas .
- If you find an attached tick, remove it promptly with fine-tipped tweezers. The CDC advises that removing a tick within 24 hours significantly reduces the risk of Lyme disease transmission.
- Contact a health-care provider and specifically mention Lyme disease concern if you develop fever, rash, or flu-like symptoms within days to weeks of a known or suspected tick exposure.
Cost and Access: What Patients Should Know
The CDC-recommended two-tier blood test for Lyme disease — an ELISA followed by a Western blot if positive — is available through primary care physicians, urgent care centers, and most hospital systems. For uninsured patients, federally qualified health centers offer sliding-scale fees at findahealthcenter.hrsa.gov.
If Lyme disease is diagnosed, early treatment with oral antibiotics is typically a 10-to-21-day course of generic doxycycline for adults, or amoxicillin or cefuroxime for children — costing under $20 for a full course at most pharmacies. Insurance coverage for Lyme disease testing and treatment is standard under most plans. Patients who are denied coverage should appeal.
One barrier worth noting: in states where Lyme disease has historically been rare, clinicians may be less likely to order Lyme testing without prompting. Patients who believe their symptoms warrant testing should advocate for themselves and ask explicitly.
What Happens Next
The geographic expansion of blacklegged ticks into previously low-risk states is expected to continue. The CAPC's 2026 forecast represents a predictive model based on canine testing data and environmental factors, with the organization reporting 94 percent historical accuracy. Ohio, Indiana, and Illinois health departments are expected to issue updated Lyme disease guidance in the coming months as case data through the 2026 season are compiled.
Researchers at Purdue University and Ohio State University are conducting ongoing surveillance studies on tick distribution and infection rates. A new Lyme disease vaccine candidate is in late-stage clinical trials and, if approved, could eventually reduce risk in high-exposure populations — though no human Lyme disease vaccine is currently approved in the United States. MedicalDaily will continue tracking geographic expansion, human case data, and prevention guidance developments as this season progresses.
The Bottom Line
Blacklegged ticks carrying Lyme disease are no longer a distant concern for residents of Indiana, Illinois, and Ohio — they are in suburban parks, forest preserves, and backyards across these states right now. The 2026 tick season is already elevated compared to prior years. The risk is not limited to deep woods or rural counties; it exists wherever there is grass, brush, deer, and suitable habitat, which now includes most of metropolitan Chicago, Columbus, Indianapolis, and Cincinnati. Standard prevention measures — repellent, permethrin, tick checks, prompt removal — are effective. Know the symptoms, mention tick exposure to your doctor, and do not assume Lyme disease is an East Coast problem.
