The National Weather Service in Chicago has issued a Flash Flood Warning for De Kalb, La Salle, and Lee counties in northern Illinois, in effect until 8:00 AM CDT Sunday. Three to six inches of rain have already fallen — the heaviest totals across Lee County — and while the heavy rain has ended for now, additional heavy rain is possible later this morning. That is a lot of water on the ground before sunrise, and it is the setup that floods creeks, drainage ditches, and low-lying neighborhoods in a hurry.
This is a live snapshot as of 5:20 AM Central (3:20 AM Pacific) on Sunday, September 20, 2026. Conditions change fast — always verify with the National Weather Service for your specific county or ZIP code.
De Kalb County, IL — Flash Flood Warning
Issued by: NWS Chicago, 5:09 AM CDT. Expires: 8:00 AM CDT Sunday.
The hazard, in NWS wording: At 5:09 AM CDT, Doppler radar indicated thunderstorms produced heavy rain across the warned area. Between 3 and 6 inches of rain have fallen. While the heavy rain has ended, additional heavy rain is possible later this morning. Flash flooding is ongoing or expected to begin shortly. Source: radar indicated.
Expected impacts: Rapid-onset flooding of creeks, streams, drainage ditches, streets, underpasses, low-lying areas, and other poor drainage areas.
Communities: Sandwich, Shabbona, Hinckley, Somonauk, Waterman, Leland, and Paw Paw are among the named locations in De Kalb County.
La Salle County, IL — Flash Flood Warning
Same warning window: issued 5:09 AM CDT, in effect until 8:00 AM CDT Sunday, with 3 to 6 inches of rain already measured across the warned area.
Communities: Mendota, Sheridan, Serena, Millington, Troy Grove, Triumph, and Prairie Center are the named locations in the warned portions of the county.
Rapid-onset is the key phrase in this alert — persons along creeks, drainage ditches, and other waterways should take immediate precautions to protect life and property. When a warning says rapid-onset, it means the water does not give you the slow-rise grace period; it jumps banks.
Lee County, IL — Flash Flood Warning
Lee County saw the highest totals in this event — the top end of the 3-to-6-inch range, per the NWS alert. Communities: Amboy, Lee, Compton, Nelson, West Brooklyn, Harmon, Sublette, Lee Center, Woodhaven Lakes, and Earlville are all named in the warning.
With six inches of rain possible in the hardest-hit spots and low-lying drainage areas explicitly called out in the impacts list, field flooding, overwhelmed roadside ditches, and water over low rural roads are the immediate concerns. Turn around, don’t drown — most flood deaths occur in vehicles, and a flooded rural road in the dark is the highest-risk spot in this whole warning.
Stay safe this morning
A Flash Flood Warning means rapid-onset flooding is imminent or may already be occurring. Turn around, don’t drown when encountering flooded roads — most flood deaths occur in vehicles.
If water enters your home: stay out of standing water where electricity may be present. Avoid the basement until water recedes and power is confirmed off. Photograph everything before cleanup — documentation matters for insurance. Then call a local restoration contractor: water left sitting starts a second wave of damage within a day.
Be especially cautious through daybreak: pre-dawn flooding is the hardest to see, and this warning’s second act — additional heavy rain possible later this morning — could land right around commute time.
What this means for restoration teams
Three to six inches is basement-flooding arithmetic in northern Illinois. The job mix out of this one: flooded basements where sump pumps lost the race (ask about battery backup and pump age on the first call — it predicts the next house on the block), seepage through foundation walls in older housing stock, saturated carpet and pad, and water wicking into finished drywall that looks fine at noon and grows a problem by Tuesday.
Mold risk clocks start the moment materials stay wet: 24 to 48 hours on saturated drywall and insulation. In the agricultural edge of these counties, outbuildings and equipment storage take water too — don’t forget the farm jobs mixed in with the residential calls.
The play: stage extraction equipment and dehumidifiers before 8 AM, because the warning expires at 8:00 AM CDT and the call volume historically starts as people wake up and walk downstairs. Keep an on-call rotation through the morning — and remember the alert explicitly allows for a second round of heavy rain later this morning, which means a second call wave. Capture address, water source, and affected areas on the first call; photo-document before mitigation; moisture-map every affected room; keep the homeowner’s payment responsibility clear in writing before work starts.
FEMA & federal assistance
If the flooding turns into a declared disaster, the FEMA Helpline is 1-800-621-3362 (7 a.m.–10 p.m. local, 7 days a week). You can also apply at DisasterAssistance.gov, through the FEMA app, or find recovery centers at fema.gov/drc. Basic eligibility: U.S. citizenship or qualified status, identity verification, proof of occupancy or ownership, and unmet needs not covered by insurance. Apply as soon as it is safe to do so.
Looking ahead
The warning expires at 8:00 AM CDT — but the story does not end there. The NWS explicitly says additional heavy rain is possible later this morning, so watch for an extension or a fresh warning if new cells develop on this saturated ground. Creeks and drainage ditches will run high through the morning and can crest after the rain stops; the water keeps moving downstream.
Demand window note for contractors: water-intrusion calls typically start within hours of water receding and keep coming for days as people discover damage — and a second round of rain would restart the whole clock.
Sources & how to verify
- NWS alert: Flash Flood Warning — NWS Chicago IL
- Issuing office: weather.gov/lot (NWS Chicago)
- To verify for your own county or ZIP: check weather.gov or your local NWS office page for the current active-alert map.
This post is for informational purposes and is not an official weather warning. Always follow instructions from local authorities and the National Weather Service.




