Hollis Park Dam
Hollis Park Dam is an earth dam located in Peoria County, Illinois, built in 1982. It carries a High hazard potential classification.
About Hollis Park Dam
The primary purpose of Hollis Park Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Hollis Park District (private). It impounds the Trib Lamarsh Creek near Mapleton.
The dam stands 51 feet tall and stretches 700 feet across, creates a reservoir covering 29 acres, has a maximum storage capacity of 820 acre-feet, and collects water from a drainage area of 534 square miles. Completed in 1982, the structure is 44 years 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 11/04/2025.
At 51 feet, this dam is taller than 93% 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.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Illinois |
| County | Peoria |
| Nearest City | Mapleton |
| River/Stream | Trib Lamarsh Creek |
| Coordinates | 40.57731, -89.74791 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 51 ft |
| Dam Height | 51 ft |
| Dam Length | 700 ft |
| Year Completed | 1982 (44 years old) |
Storage & Hydraulics
| NID Storage | 820 acre-ft |
| Max Storage | 820 acre-ft |
| Normal Storage | 335 acre-ft |
| Surface Area | 29 acres |
| Drainage Area | 534 sq mi |
| Max Discharge | 4,686 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | HOLLIS PARK DISTRICT |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Not Available |
| Last Inspection | 11/04/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL01005 |
| Federal ID | IL01005 |
| More Info | State Dam Safety Program |