Ticks are most prevalent in the eastern United States, across central and northern Europe, and in any landscape that combines warm temperatures, high humidity, and abundant wildlife hosts. Within those broad regions, tick density varies dramatically at the local level. A shady forest edge with deep leaf litter can harbor several times more ticks than an open lawn just a few yards away. Understanding both the big-picture geography and the small-scale habitats where ticks concentrate helps you gauge your actual risk.
Highest-Risk Regions in the United States
The blacklegged tick (also called the deer tick) is widely distributed across the entire eastern United States, from Maine to Florida and as far west as Minnesota and Texas. Within that range, the densest populations cluster in the Northeast, the upper Midwest, and the mid-Atlantic states. These are the same regions that report the vast majority of Lyme disease cases each year. The western blacklegged tick fills a similar role along the Pacific coast, with particularly high numbers in northern California.
The lone star tick, which can trigger a red meat allergy and carries several other diseases, is established throughout the Northeast, South, and Midwest. Its range has been creeping northward and westward in recent years, though ticks spotted at the edges of that expanding territory may not yet have stable enough conditions to form permanent populations.
The American dog tick and the Rocky Mountain wood tick round out the major species. The dog tick is found east of the Rockies and in parts of the Pacific coast, while the wood tick occupies the northern Rockies and parts of southwestern Canada. Each species carries different diseases, so knowing which ticks live in your area matters more than simply knowing “ticks are nearby.”
Tick Prevalence Across Europe and Beyond
Europe’s dominant tick species, commonly called the castor bean tick, spans the continent from Portugal to Scandinavia. A large review of European surveillance data found that roughly 11% of these ticks carried the bacteria responsible for Lyme disease, with the highest infection rates in eastern Europe. In Bulgaria, Ukraine, and Romania, 27% to 37% of sampled ticks tested positive. The United Kingdom had some of the lowest rates, under 4.2%.
Climate change is actively reshaping this map. Warming temperatures have pushed ticks into northern Scandinavia and to higher altitudes in the Alps and Carpathian mountains, areas where they were previously unable to survive winter. Similar range expansions are documented in parts of Asia, particularly across Russia, China, Japan, and South Korea, where tick-borne encephalitis and other infections are growing public health concerns.
What Drives Tick Populations Locally
Two factors matter more than any others for tick survival: humidity and the presence of large mammal hosts, especially deer.
Ticks are extremely vulnerable to drying out. They need moist microclimates to survive between blood meals, which is why they thrive in leaf litter, shaded underbrush, and forest floors where humidity stays high. Tick larvae become active when temperatures rise above roughly 10°C (50°F), and eggs actually survive better at warmer temperatures as long as moisture levels remain adequate. Some species can tolerate brief exposure to extreme cold, surviving temperatures as low as -24°C (-11°F) for short periods and -13°C (9°F) for up to three months, which explains how they persist through harsh winters in the northern U.S. and Canada.
White-tailed deer are the single biggest driver of tick abundance in eastern North America. Over 90% of adult female blacklegged ticks feed on deer. One well-studied residential community in Connecticut demonstrated this connection clearly: when deer density was reduced from roughly 40 to 50 deer per square kilometer down to about 5 per square kilometer, tick abundance dropped 76%, tick infection rates fell nearly 50%, and resident-reported Lyme disease cases declined by 80%. Nymphal tick density correlated strongly with deer density, and researchers estimated that getting deer populations below about 5 per square kilometer was the threshold needed to meaningfully reduce human disease risk.
Where Ticks Hide in Your Yard
You don’t need to hike deep into the woods to encounter ticks. The transition zone between your lawn and adjacent woods, often called the forest edge, is one of the most tick-dense habitats around homes. A study tracking tick counts across residential properties found that areas where homeowners blew leaves into the forest edge had a median of 14.5 blacklegged tick nymphs per sampling visit, compared to just 4 in natural forest edge and 4 in deeper woods. Leaf blowing essentially creates an ideal tick habitat: a thick, moist layer of organic material right at the boundary where people, pets, and wildlife all cross paths.
Lone star ticks showed a different pattern. Nearly half of the adults were collected from deeper forest plots, with lower numbers at the edges. This means your risk profile depends partly on which tick species lives in your area. In general, though, the riskiest spots on a residential property are shaded edges with leaf litter, woodpiles, stone walls, and overgrown ground cover. Open, sunny, mowed lawn is the lowest-risk zone.
City Parks vs. Rural Forests
Urban green spaces are not tick-free. A study comparing tick populations in Warsaw’s city parks to the natural forests near Białowieża, Poland, found ticks present in both settings. Tick abundance in natural forests was about 40% higher overall than in city parks and urban forests. Within any given area, forests supported roughly twice the tick density of fenced parks, largely because of differences in nymph numbers. Adult tick counts were similar between the two settings.
The takeaway: city parks in tick-endemic regions still carry real risk, particularly wooded sections with ground-level vegetation. Paved paths and maintained turf are lower risk, but stepping off the trail into brush or sitting on leaf-covered ground puts you back in tick territory.
When Ticks Are Most Active
Tick season is not a single window. In the northeastern and upper midwestern U.S., nymphal blacklegged ticks peak in early summer (roughly May through July), while larvae peak in late summer (August into September). Adults are most active in fall and again in early spring. Nymphs are the life stage responsible for the most human disease transmission because they’re small enough to go unnoticed on your skin and are actively feeding during the months when people spend the most time outdoors.
In the southeastern U.S., milder winters allow ticks to remain active for a longer stretch of the year, and some species feed on hosts nearly year-round. On the West Coast, the western blacklegged tick follows a slightly different calendar, with nymphs active in spring and early summer, particularly in the leaf litter of oak woodlands. Regardless of where you live within tick range, the safest assumption is that any day above 40°F (4°C) with adequate ground moisture is a day ticks could be actively seeking a host.