Identification of Unmapped Special Flood Hazard Areas in Illinois

Presented here are maps of each of Illinois’ 102 counties illustrating stream reaches with potential flood risk for which Special Flood Hazard Areas (SFHAs) have not been identified on Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) as of July 1, 2007. Tabular data providing stream names and number of unmapped stream miles are listed here. More on our study approach is listed in the contract report.

Select a county of interest to view and/or download the map. Please see our disclaimer.


FEMA publishes FIRMs showing SFHAs, which have a 1 percent chance of being inundated in any given year. The nationwide identification of SFHAs was initiated with the signing of the Flood Insurance Act of 1968.  Illinois Administrative Code defines state oversight of floodways for streams that drain 10 square miles (sq. mi.) or more in rural areas or 1 sq. mi. or more in urban or urbanizing areas.  This general guidance has been used in preparing Illinois FIRMs to identify streams that pose a flood hazard.  Many SFHAs for streams meeting these criteria have not been identified on Illinois FIRMs, however. There are streams in rural and urban areas meeting the criteria for which SFHAs have never been identified, and there are urban areas where community annexation is expanding into areas mapped according to rural guidelines of a 10 sq. mi. drainage area. Unmapped SFHAs pose a flood risk that is has not been communicated to the public, floodplain managers, or elected officials.  In order to bridge this gap in Illinois, a screening process was developed, and streams having potential flood risk for which SFHAs have not been mapped were identified for each Illinois county.

This project was sponsored by the Federal Emergency Management Agency, through the Map Modernization Management Support Best Practices Award for Federal Fiscal Year 2006, awarded to the Illinois Department of Natural Resources under Cooperating Technical Partner (CTP) Agreement EMC-2006-CA-7023.

Adams County Hancock County Morgan County
Alexander County Hardin County Moultrie County
Bond County Henderson County Ogle County
Boone County Henry County Peoria County
Brown County Iroquois County Perry County
Bureau County Jackson County Piatt County
Calhoun County Jasper County Pike County
Carroll County Jefferson County Pope County
Cass County Jersey County Pulaski County
Champaign County Jo Daviess County Putnam County
Christian County Johnson County Randolph County
Clark County Kane County Richland County
Clay County Kankakee County Rock Island County
Clinton County Kendall County Saline County
Coles County Knox County Sangamon County
Cook County (south) Lake County Schuyler County
Cook County (north) LaSalle County Scott County
Crawford County             Lawrence County Shelby County
Cumberland County Lee County St. Clair County
DeKalb County Livingston County Stark County
DeWitt County Logan County Stephenson County
Douglas County Macon County Tazewell County
DuPage County Macoupin County Union County
Edgar County Madison County Vermilion County
Edwards County Marion County Wabash County
Effingham County Marshall County Warren County
Fayette County Mason County Washington County
Ford County Massac County             Wayne County
Franklin County McDonough County White County
Fulton County McHenry County Whiteside County
Gallatin County McLean County Will County
Greene County Menard County Williamson County
Grundy County Mercer County Winnebago County
Hamilton County Monroe County Woodford County
Montgomery County