River IL

Flat River

Illinois • 37.8352, -90.5472

Reviewed mapped path Updated Dec 30, 2025

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USGS and NOAA data is for informational purposes. Source notes

Length

15 mi

24 km

Elevation

1,111′ → 659′

452 ft drop

Stream Order

Medium River

Slope

0.58%

30.6 ft/mi

Drainage

45 mi²

118 km²

Avg Flow

-- cfs

1.1 mph velocity

Path to Mouth

315 mi

507 km to ocean

Classification

Tributary

Mid-reach

Elevation Profile

Water Quality

Data from EPA Water Quality Portal (USGS, EPA, state agencies).

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Data from USGS & NOAA for informational purposes only. Read source and safety notes

Access Sites on Flat River

There are 3 linked public-access records for Flat River.