Connecticut Tick Risk by County: What the 2025 State Data Shows

Most tick advice is written for the whole country, which makes it nearly useless if you live in Connecticut. This state has its own numbers — collected every year, by the state, from real field sites — and they say something more specific than "check yourself for ticks."

The Connecticut Agricultural Experiment Station runs an active tick surveillance program: researchers drag a square meter of cloth through vegetation at 40 publicly accessible locations across all eight counties, spring through fall, then test what they collect. In 2025 that produced more than 10,000 ticks, screened for five human disease-causing pathogens.

What's actually in Connecticut ticks

These are statewide infection rates in blacklegged ticks — the species that transmits Lyme disease. Note the gap between adults and nymphs; it matters more than it looks.

Better than half of adult blacklegged ticks in Connecticut carry the Lyme bacterium. That is not a fringe risk — it's a coin flip on any adult tick you find.

Why the lower nymph number is the scarier one

Nymphs test positive at 25% versus 55% for adults, so the nymph looks like the safer encounter. It isn't. A nymph is roughly the size of a poppy seed, it's most active in late spring and early summer when people are outside constantly, and it's routinely missed during a tick check. Adults are the size of a sesame seed and far easier to spot and remove before transmission.

Lower infection rate, dramatically higher chance of going unnoticed. That's the trade, and it's why late spring is the season that actually deserves your attention.

Where the ticks are densest

Density varies by county, and the 2025 results split along an interesting line — the county with the most adults isn't the county with the most nymphs.

If you're in Fairfield County, roughly two out of three adult female blacklegged ticks are carrying the Lyme bacterium — well above the 55% statewide figure. New Haven County nymphs run at 32% against a 25% state average, which matters because nymphs are the ones you don't see.

Connecticut now has four tick species worth knowing

The blacklegged tick is the one most people can name, but 2025 collections turned up four species, and two of them are relatively new arrivals here.

Lone star ticks, native to the southern United States, have now been detected in Fairfield, Middlesex, New Haven, New London and Windham counties. The invasive longhorned tick has been confirmed in Fairfield, Middlesex, New Haven and New London counties. Both are recent enough that most Connecticut tick advice written even a few years ago doesn't mention them.

Read those collection totals carefully. Longhorned ticks topping the list doesn't mean they've overtaken blacklegged ticks across Connecticut — the state says single sampling events produced large larval clusters that skew the count. Anyone citing that number as proof of an invasion is misreading it.

What the state actually recommends

• Do a routine tick check after any time outdoors — not just after hiking.
• Wear long sleeves and pants in light-colored, tightly woven fabric, which makes ticks easier to see.
• Tuck pant legs into socks in tick-prone areas.
• Consider permethrin-treated clothing, which both repels and kills ticks. Follow the product label.

Worth emphasizing that the state's own guidance leads with personal prevention, not yard treatment. Tick checks and treated clothing are free or nearly free, and they address the exposure that actually produces most infections.

When a yard treatment is worth considering

Property treatment becomes a reasonable conversation when your yard backs onto woods, leaf litter or stone walls, when you have kids or pets in the yard daily through nymph season, or when you're finding ticks on people and animals repeatedly despite doing the basics. A treatment reduces tick pressure in the treated area — it doesn't replace tick checks, and no honest provider will tell you otherwise.

If you go that route, ask what product is applied, exactly where, and how long before kids and pets can return to the yard. That re-entry interval comes from the product label, and any licensed applicator should be able to state it without hesitating.

How to use this if you live here

Find your county in the tables above. If you're in New London, expect high adult density in fall. Litchfield, watch nymphs in late spring. Fairfield, treat any adult female tick you find as more likely infected than not. And statewide, the most valuable thing on this page is still the least expensive one: check yourself after you come inside.

Connecticut updates these numbers every year, usually in March. We'll update this page when the next release lands.