Current Flu Activity in Illinois

As of spring 2026, flu season continues across Illinois and the broader Midwest. While national flu activity is declining from its winter peak, Illinois often sees a longer tail of flu activity that extends into April.

Check the latest ILI rates and trend charts on our Illinois flu dashboard, updated every Friday with CDC ILINet data.

What the Numbers Mean

The CDC’s ILINet network tracks the percentage of outpatient medical visits where patients present with influenza-like illness (ILI) — defined as fever plus cough or sore throat. This gives us a weekly signal of how active flu is across the state.

Our Illinois flu page shows:

Current activity level (Low, Moderate, High, or Very High)
Weekly trend — is flu increasing, stable, or decreasing?
Comparison to the national average — is Illinois above or below?
Nearby state data — how do neighbors compare?

Illinois vs. Neighboring Midwest States

The Midwest often moves together on flu, but there can be meaningful differences between states. Compare Illinois to:

Indiana flu activity — Eastern neighbor
Wisconsin flu activity — Northern neighbor
Iowa flu activity — Western neighbor
Missouri flu activity — Southern neighbor
Kentucky flu activity — Southeast

When Does Flu Season End in Illinois?

Flu season in Illinois typically runs from October through May, with peak activity between December and February. The timing can vary — some years see a second smaller wave in March-April, especially if a different flu strain becomes dominant late in the season.

We track the full 52-week trend on the Illinois flu page, so you can see exactly where in the curve we are.

What Else Is Going Around in Illinois?

Illinois COVID-19 activity — Emergency department visit data
Illinois RSV activity — Hospital admission rates
Illinois measles cases — 2026 case tracking
Illinois MMR vaccination rate — Kindergarten coverage
What’s going around in Illinois? — Full state health dashboard

About This Data

Data from the CDC’s ILINet surveillance network, accessed via the Delphi Epidata API. Updated weekly on Fridays. See our methods page for full details.

Updated weekly. Last update: April 3, 2026.