FEMA claims · Winnebago County
Most basement flooding in Winnebago County happens outside the flood zone
We pulled every basement flood-insurance claim FEMA has released for Winnebago County, Illinois: 923 claims on homes with a finished or unfinished basement. Here is where the water actually showed up.
15% of those claims came from homes outside the mapped floodplain.
That is 131 of 856 claims with a rated flood zone. Look only at claims caused by rainfall or snowmelt soaking in, the seepage kind rather than a river coming up, and the share climbs to 13% (38 of 300).
The real number is almost certainly higher
Every claim here comes from a home that carried flood insurance. Near a floodplain, a federally backed mortgage all but forces you to buy it. Away from one, almost nobody does. So the homes in this data lean heavily toward the flood zone, and the out-of-zone basements that flooded without insurance never show up at all.
So read 15% as a floor. It is the share we can prove for Winnebago County, and the true share of basement flooding outside the mapped zone is higher. This is not a flooding rate, so please do not quote it as one.
Winnebago County claims by rated flood zone
The zone FEMA had each property in when it flooded. Zones starting with A or V are the Special Flood Hazard Area, where flood insurance is effectively mandatory. Everything else sits outside it.
| Flood zone | Risk category | Basement claims |
|---|---|---|
| AE | High-risk (SFHA) | 341 |
| A07 | High-risk (SFHA) | 179 |
| A | High-risk (SFHA) | 90 |
| No rated zone | Unrated | 67 |
| X | Outside the flood zone | 59 |
| A11 | High-risk (SFHA) | 54 |
| C | Outside the flood zone | 41 |
| A06 | High-risk (SFHA) | 41 |
Where this comes from
The source is FEMA's NFIP redacted claims dataset (openFEMA FimaNfipClaims v2), filtered to buildings recorded with a finished or unfinished basement. Crawlspaces are out. A property counts as inside the floodplain when its rated zone starts with A or V, the Special Flood Hazard Area. Everything else is outside. 67 claims carry no rated zone, so we report them but keep them out of the percentage.
This is county data, not city. FEMA redacts the city field, so Winnebago County is the finest honest level we can show. It takes in suburbs and unincorporated land, and the cities we cover inside it map to this county.
The claims run from 1978 to 2025.
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