Ticks in Illinois

Ticks are active in Illinois whenever the ground is not frozen, led by the Lyme-carrying deer tick. TickZone scores all 1294 Illinois towns every morning, so risk stays local: pick your town for today's number, a 7-day outlook, and what's driving it.

Tick season in Illinois

Tick season in Illinois runs whenever the ground is not frozen, roughly March through November, with two peaks. Nymph deer ticks, the poppy-seed-sized stage that causes most Lyme cases, peak from late May through July. Adult deer ticks make a second push in October and November, and on any winter day above about 40 F they can quest again. American dog ticks are busiest from April through July.

Generalized for the Northeast and Upper Midwest Lyme belt.
Life stageJFMAMJJASOND
Deer tick nymphs
Deer tick adults
American dog tick
Lone star tick
Peak Active
Generalized for the Northeast and Upper Midwest Lyme belt. Activity windows by life stage from TickEncounter (Univ. of Rhode Island) and the Northeast Regional Center for Excellence in Vector-Borne Diseases. Any warm spell can wake ticks earlier than the calendar suggests.

Those are averages, and any single week can run hotter or colder than the calendar suggests. The daily score on every town page folds the season, the weather, and local habitat into one number each morning, so it is the safer way to time yard work, hikes, and pet prevention.

Highest-risk towns in Illinois (2026)

Illinois's highest-risk towns are spread across several counties, led by Marshall. The top 10 towns run 79 to 95 percent forest, ranked at peak season so the list stays stable.

  1. 1Hopewell Marshall CountyModerate at peak
  2. 2Rockwood Randolph CountyModerate at peak
  3. 3Tower Lakes Lake CountyModerate at peak
  4. 4Norwood Peoria CountyModerate at peak
  5. 5Trout Valley McHenry CountyModerate at peak
  6. 6Kenilworth Cook CountyModerate at peak
  7. 7Thebes Alexander CountyModerate at peak
  8. 8Elsah Jersey CountyModerate at peak
  9. 9Valley City Pike CountyModerate at peak
  10. 10Leland Grove Sangamon CountyModerate at peak

See the riskiest towns in every state →

All Illinois towns, by county

Adams County · 14 towns

Alexander County · 5 towns

Bond County · 8 towns

Boone County · 5 towns

Brown County · 4 towns

Bureau County · 23 towns

Calhoun County · 5 towns

Carroll County · 7 towns

Cass County · 5 towns

Champaign County · 23 towns

Christian County · 13 towns

Clark County · 4 towns

Clay County · 6 towns

Clinton County · 14 towns

Coles County · 6 towns

Cook County · 119 towns · 2/100k Lyme

Crawford County · 6 towns

Cumberland County · 4 towns

De Witt County · 7 towns

DeKalb County · 12 towns

Douglas County · 8 towns

DuPage County · 30 towns · 4/100k Lyme

Edgar County · 8 towns

Edwards County · 4 towns

Effingham County · 10 towns

Fayette County · 7 towns

Ford County · 9 towns

Franklin County · 14 towns

Fulton County · 20 towns · 18/100k Lyme

Gallatin County · 7 towns

Greene County · 9 towns

Grundy County · 12 towns

Hamilton County · 5 towns

Hancock County · 15 towns

Hardin County · 3 towns

Henderson County · 8 towns

Henry County · 14 towns

Iroquois County · 21 towns

Jackson County · 11 towns

Jasper County · 7 towns

Jefferson County · 9 towns

Jersey County · 6 towns

Jo Daviess County · 10 towns · 41/100k Lyme

Johnson County · 7 towns

Kane County · 23 towns · 4/100k Lyme

Kankakee County · 19 towns

Kendall County · 8 towns · 5/100k Lyme

Knox County · 14 towns

Lake County · 46 towns · 5/100k Lyme

LaSalle County · 24 towns · 7/100k Lyme

Lawrence County · 5 towns

Lee County · 12 towns

Livingston County · 14 towns

Logan County · 10 towns

Macon County · 12 towns

Macoupin County · 27 towns

Madison County · 27 towns

Marion County · 13 towns

Marshall County · 8 towns

Mason County · 9 towns

Massac County · 3 towns

McDonough County · 10 towns

McHenry County · 27 towns · 7/100k Lyme

McLean County · 21 towns

Menard County · 5 towns

Mercer County · 10 towns

Monroe County · 6 towns

Montgomery County · 20 towns

Morgan County · 10 towns

Moultrie County · 6 towns

Ogle County · 13 towns

Peoria County · 15 towns · 8/100k Lyme

Perry County · 6 towns

Piatt County · 8 towns

Pike County · 17 towns

Pope County · 2 towns

Pulaski County · 7 towns

Putnam County · 6 towns

Randolph County · 14 towns

Richland County · 5 towns

Rock Island County · 15 towns

Saline County · 6 towns

Sangamon County · 25 towns

Schuyler County · 4 towns

Scott County · 7 towns

Shelby County · 11 towns

St. Clair County · 25 towns

Stark County · 4 towns

Stephenson County · 11 towns

Tazewell County · 16 towns · 5/100k Lyme

Union County · 6 towns

Vermilion County · 21 towns

Wabash County · 4 towns

Warren County · 5 towns

Washington County · 12 towns

Wayne County · 9 towns

White County · 10 towns

Whiteside County · 11 towns · 11/100k Lyme

Will County · 25 towns · 3/100k Lyme

Williamson County · 15 towns

Winnebago County · 11 towns · 5/100k Lyme

Woodford County · 15 towns

Illinois tick questions

Are there ticks in Illinois?
Yes. Illinois has ticks in every county, led by the deer tick (blacklegged tick) that spreads Lyme disease, along with the American dog tick and the lone star tick. They are active whenever the ground is not frozen, and today 584 of the state's 1294 towns are at moderate or high tick risk on TickZone's daily score.
What types of ticks live in Illinois?
Illinois has the deer tick (blacklegged tick), which carries Lyme disease; the American dog tick; and the lone star tick, which is reported in the state and causes alpha-gal syndrome. See the Illinois tick identification chart for photos and how to tell them apart.
When does tick season start and end in Illinois?
In Illinois, ticks are active whenever the ground is not frozen, roughly March through November. Nymph deer ticks peak in June and July and cause most Lyme cases, and adult ticks have a second peak in the fall. On any winter day above freezing, adult ticks can still bite.
When is flea and tick season?
Flea and tick season generally runs from early spring through late fall, peaking in the warm summer months. In Illinois, start prevention for pets and people in March and keep it up through November, since ticks can bite on any mild day.
Which tick carries Lyme disease in Illinois?
The deer tick, also called the blacklegged tick, is the tick that spreads Lyme disease in Illinois. The American dog tick and lone star tick do not carry Lyme.