Pennsylvania consistently ranks as the state with the most tick-borne disease in the United States, accounting for 29.2% of all reported Lyme disease cases between 2016 and 2019. Seven of the ten counties most affected by Lyme disease are in Pennsylvania. New Jersey (11.7%) and New York (11.6%) follow closely behind. While no single agency counts every tick in every state, disease surveillance data and ecological surveys point to the Northeast and Upper Midwest as the regions with the densest, most disease-carrying tick populations in the country.
Why Pennsylvania Leads the Pack
Pennsylvania’s combination of geography, climate, and land use creates near-perfect conditions for ticks. The state has vast stretches of deciduous forest interspersed with suburban development, exactly the kind of fragmented woodland where ticks thrive. Forest fragmentation creates more “edge habitat,” the border zones between woods and open areas where deer and mice travel freely. White-footed mice are especially important because they’re one of the primary carriers of the bacteria that cause Lyme disease, and their populations boom in fragmented forests where predator diversity is low.
The state’s large white-tailed deer population compounds the problem. Deer are the primary host for adult blacklegged ticks (also called deer ticks), and Pennsylvania has one of the highest deer densities in the nation. More deer means more ticks completing their life cycle and laying eggs, which means more larvae and nymphs the following season.
The Northeast and Upper Midwest Hotspot
The blacklegged tick is widely distributed across the entire eastern United States, but density varies enormously. The highest concentrations cluster in two regions: the Northeast (from Virginia up through New England) and the Upper Midwest (Wisconsin and Minnesota). These areas share a common history. Over the past century, farmland in the Northeast reverted to forest, creating a patchwork of reforested areas that allowed white-tailed deer populations to explode. That reforestation, combined with suburban sprawl pushing homes into wooded areas, set the stage for the tick crisis that exists today.
Connecticut offers a striking example of just how tick-saturated the Northeast has become. In 2025, the Connecticut Agricultural Experiment Station collected over 10,600 ticks from just 40 publicly accessible sites across the state’s eight counties. Of the nymphal blacklegged ticks they tested, 43.8% carried at least one disease-causing pathogen, and nearly one in four (24.7%) carried the bacterium responsible for Lyme disease. About 8.6% carried two or more pathogens simultaneously.
It’s Not Just About Lyme Disease
Lyme disease gets the most attention, but ticks transmit a growing list of illnesses. Connecticut’s surveillance data highlights the scope: beyond Lyme, significant percentages of tested nymphs carried pathogens that cause babesiosis (12.6%), anaplasmosis (4.5%), and a relapsing fever caused by a related bacterium (2.0%). Some ticks carried multiple infections at once, meaning a single bite could potentially transmit more than one disease.
The lone star tick, a more aggressive species common in the Southeast and Mid-Atlantic, brings its own set of problems. This tick’s bite can trigger alpha-gal syndrome, an allergic reaction to red meat and other mammal-derived products. The geographic footprint of alpha-gal syndrome stretches across a wide band of the southern, midwestern, and mid-Atlantic states, with particularly high rates in parts of Virginia, Kentucky, Oklahoma, Arkansas, Missouri, Tennessee, and North Carolina. Suffolk County, New York, alone accounted for 4% of all suspected cases nationwide between 2017 and 2022, with 3,746 cases identified. Virginia’s Charlotte County had the highest per-capita rate in the country.
Suburban Green Spaces Carry Surprising Risk
You don’t need to hike deep into the woods to encounter ticks. Research in the Northeast has found that built environments containing green spaces, vegetated walkways, and nature preserves carry tick encounter risks equivalent to the highest reported levels in fully natural settings. That means your local park trail, a greenway through your neighborhood, or the wooded edge of a school playground can be just as risky as a backcountry trail.
This is partly why suburban counties in Pennsylvania, New Jersey, and Connecticut report such high tick-borne disease numbers. People living in these areas interact with tick habitat daily, often without realizing it. A short walk through leaf litter or tall grass at the edge of a yard is enough exposure for a tick to latch on.
When Tick Season Peaks
Tick activity follows a predictable seasonal pattern, but the specifics depend on where you live. Across most of the country, spring marks the start of what people recognize as tick season, with May historically being the single worst month of the year. This is when nymphal blacklegged ticks, the tiny juvenile stage most responsible for transmitting Lyme disease, are most active. Nymphs are roughly the size of a poppy seed, making them easy to miss on your skin.
Fall brings a second surge, particularly in the Northeast, as adult blacklegged ticks become active and search for hosts through September, October, and November. In the Deep South and along the West Coast, ticks remain active even through winter months when temperatures stay mild enough. In practical terms, if you live anywhere in the eastern half of the country, tick vigilance from April through November covers the primary risk window. In warmer states, year-round awareness is more appropriate.
State-by-State Risk at a Glance
- Highest overall tick-borne disease burden: Pennsylvania, New Jersey, New York, Connecticut, Massachusetts, Virginia, Maryland
- Highest alpha-gal syndrome rates: Virginia, Kentucky, Oklahoma, Arkansas, Missouri, Tennessee, North Carolina
- Upper Midwest hotspot: Wisconsin and Minnesota, with blacklegged tick populations expanding steadily into new counties
- Expanding range: The blacklegged tick continues to establish itself in counties across the Southeast and Midwest where it was previously unrecorded. A county not yet labeled “established” by the CDC does not mean ticks are absent.
Pennsylvania’s combination of high tick density, large human population living in suburban-forest interfaces, and abundant deer habitat keeps it at the top of most rankings. But the broader picture is that tick populations are dense across a wide swath of the eastern U.S., and the borders of that region keep pushing outward.