FleaDates › Tick season › Illinois
Midwest · IL
When are ticks active in Illinois?
Ticks in Illinois are typically active early March to late November, heaviest Apr–Oct — and adult blacklegged ticks can surface on any mild winter day.
Ticks to know in Illinois
The blacklegged (deer) tick has settled into northern and western Illinois woodlands and river corridors, American dog ticks work the tall grass along trail edges, and lone star ticks turn up mainly in the southern counties. Pressure starts registering in March, holds highest from May into September, and stays worth taking seriously through October and November, when adult blacklegged ticks move about on mild days. A slow pass with your hands over ears, armpits and between toes after any walk in leaf litter catches most of what your dog picks up.
Wherever the calendar sits this month, the habit that actually catches ticks is the after-walk check: ears, collar line, armpits, between the toes. Prevention plus checks beats either alone.
Month-by-month tick activity in Illinois
| Month | Typical activity | Average temperature |
|---|---|---|
| January | Quiet | 26.5°F |
| February | Quiet | 30.7°F |
| March | Moderate | 41.4°F |
| April | High | 52.6°F |
| May | Peak | 63.4°F |
| June | Peak | 72.7°F |
| July | Peak | 76.4°F |
| August | Peak | 74.6°F |
| September | Peak | 67.6°F |
| October | High | 55.3°F |
| November | Moderate | 42.5°F |
| December | Quiet | 31.7°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 3 weather stations near Illinois's larger cities, using the ~40°F activity threshold reported in published tick research. Real years run early or late with the weather.
Fleas peak later. Illinois flea season typically runs early April to early November — see the Illinois flea season page.
Frequently asked questions
When does tick season start in Illinois?
Around early March in a typical year, once temperatures clear roughly 40°F — noticeably earlier than flea season. A February thaw can bring ticks out ahead of schedule.
What ticks live in Illinois?
The species dog owners most often meet in Illinois: blacklegged (deer) tick, American dog tick, lone star tick. The blacklegged (deer) tick has settled into northern and western Illinois woodlands and river corridors, American dog ticks work the tall grass along trail edges, and lone star ticks turn up mainly in the southern counties. Pressure starts registering in March, holds highest from May into September, and stays worth taking seriously through October and November, when adult blacklegged ticks move about on mild days. A slow pass with your hands over ears, armpits and between toes after any walk in leaf litter catches most of what your dog picks up.
Do I need tick prevention in winter in Illinois?
Yes. Ticks overwinter under leaf litter and snow rather than dying off, and mild spells wake them — which is why veterinary organizations recommend year-round parasite prevention. The calendar shows when pressure peaks, not when protection can lapse.
What about fleas in Illinois?
Fleas run on a warmer calendar — in Illinois that's early April to early November. See the Illinois flea season page for that month-by-month picture.