Lake Decatur Dam

About Lake Decatur Dam

The primary purpose of Lake Decatur Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by City Of Decatur (local government). It impounds the Sangamon River near Decatur.

The dam stands 33 feet tall and stretches 1,728 feet across, creates a reservoir covering 3,335 acres, has a maximum storage capacity of 57,520 acre-feet, and collects water from a drainage area of 906 square miles. Completed in 1922, the structure is over a century old.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. An emergency action plan is in place for this dam. The most recent inspection on record was 09/08/2025.

At 33 feet, this dam is taller than 78% of dams nationwide.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Illinois dam safety program can provide more specific information about emergency planning for this structure.

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