A red sun low over Slim Lake through wildfire haze, its reflection a column of orange on the water

Reservoirs in Illinois

67 of 594 measured Illinois lakes (11%) are man-made reservoirs in the USACE National Inventory of Dams. 52 carry a High or Significant hazard rating.

Reading the Illinois reservoir landscape

67 reservoirs in Illinois appear in the USACE National Inventory of Dams. That's a meaningful share — reservoir lakes carry their own ecology and access patterns distinct from natural lakes, including managed water levels, drawdowns timed to the dam's purpose, and shoreline mix dominated by structures built post-impoundment.

Recreation is the headline purpose for the largest share of Illinois's reservoirs — lakes where the dam exists explicitly to create surface water for fishing, boating, and adjacent shoreline development. Pool levels are typically maintained more stably than at flood-control or hydro reservoirs, which supports fixed-dock access, consistent boat ramps, and the kind of shoreline economy that natural-lake counterparts in the state share.

The USACE National Inventory of Dams (NID) catalogs every dam in the United States above a size threshold — typically 25 feet in height or 50 acre-feet in maximum storage, plus all dams classified as high-hazard regardless of size. The reservoir records below pull NID fields (year built, hazard class, maximum storage, surface area at normal pool, dam length, primary purpose) and pair them with water-quality data where the impoundment also appears in EPA's lake-monitoring inventory.

Why these Illinois reservoirs were built

Recreation

Water Supply

Flood Risk Reduction

Other

Debris Control

Navigation

Total reservoirs

45,019

Total surface acres

560,906

Normal storage (ac-ft)

High or Significant hazard

All 67 Illinois reservoirs (by surface area)

Reservoir	County	Surface area	Year built	Purpose	Hazard
Carlyle Lake	Clinton	24,580 ac	1966	Flood Risk Reduction	High
Lake Springfield	Sangamon	4,224 ac	1933	Recreation	High
Decatur Lake	Macon	3,335 ac	1922	Recreation	High
Kinkaid Lake	Jackson	2,500 ac	1972	Recreation	High
Lake of Egypt	Williamson	2,265 ac	1962	Other	High
Lou Yaeger Lake	Montgomery	1,410 ac	1966	Recreation	High
Mattoon Lake	Cumberland	980 ac	1957	Recreation	Significant
Governor Bond Lake	Bond	900 ac	1969	Recreation	Significant
Otter Lake	Macoupin	760 ac	1969	Recreation	Significant
Raccoon Lake	Marion	730 ac	1943	Water Supply	High
Sara Lake	Effingham	586 ac	1957	Recreation	Significant
Jacksonville Lake	Morgan	477 ac	1939	Recreation	Significant
Holiday Shores Lake	Madison	345 ac	1965	Recreation	Significant
Centralia Lake	Marion	300 ac	1911	Recreation	Significant
Mauvaise Terre Lake	Morgan	262 ac	1923	Recreation	High
Round Lake	Lake	242 ac	1945	Recreation	Significant
Paradise Lake	Coles	174 ac	1929	Recreation	High
George Lake	Rock Island	167 ac	1962	Recreation	High
Kinmundy New Lake	Marion	100 ac	1998	Recreation	High
Glendale Lake	Pope	84 ac	1938	Recreation	Significant
Salem Lake	Marion	78 ac	1912	Recreation	High
Vienna Correctional Center Lake	Johnson	74 ac	1964	Recreation	Low
Loch Lomond Lake	Lake	72 ac	1958	Recreation	Significant
Maple Lake	Cook	60 ac	1918	Recreation	Significant
Nashville City Lake	Washington	52 ac	1935	Recreation	High
Greenfield Lake	Greene	52 ac	1959	Water Supply	Significant
Vernor Lake	Richland	45 ac	1924	Recreation	Significant
Palmyra-Modesto Lake	Macoupin	37 ac	1965	Water Supply	Significant
Midlothian Lake	Cook	30 ac	1975	Flood Risk Reduction	High
One Horse Gap Lake	Pope	29 ac	1973	Recreation	Significant
Pounds Hollow Lake	Gallatin	28 ac	1939	Recreation	Significant
Fairfield Lake	Wayne	18 ac	1979	Water Supply	Low
Tecumseh Lake	Hardin	13 ac	1976	Recreation	Low
Woods Creek Lake	McHenry	9.3 ac	1926	Recreation	High
Mermet Lake	Massac	0.7 ac	1950	Recreation	Low
Lake Arlington	Cook	—	1977	Flood Risk Reduction	High
Bull Frog Lake	Cook	—	1958	Recreation	Significant
Papoose Lake	Cook	—	1956	Recreation	Significant
Sauk Lake	Cook	—	1923	Recreation	Low
Doughnut Lake	Cook	—	1987	Flood Risk Reduction	High
Tampier Lake	Cook	—	1964	Recreation	Significant
Lake Calumet	Cook	—	1960	Navigation	High
Silver Lake	McHenry	—	1929	Recreation	Low
Saganashkee Slough Lake	Cook	—	1948	Recreation	Significant
Bullfrog Lake	Cook	—	1958	Recreation	Significant
Hastings Lake	Lake	—	1955	Recreation	Low
Galena Lake	Jo Daviess	—	1974	Recreation	High
Timber Lake	Lake	—	1949	Recreation	Low
Randolph Lake	Randolph	—	1960	Recreation	Significant
Sam Dale Lake	Wayne	—	1960	Recreation	Significant
Wayne City Lake	Wayne	—	1983	Water Supply	Low
Timber Lake	Carroll	—	1960	Recreation	Significant
Bass Lake	Lee	—	1971	Recreation	Low
Woodhaven Lake	Lee	—	1975	Recreation	Low
Shabbona Lake	DeKalb	—	1974	Other	Low
Glenn Shoals Lake	Montgomery	—	1978	Flood Risk Reduction	Significant
Newton Lake	Jasper	—	—	Other	Significant
Marie Lake	Lake	—	—	Debris Control	High
Highland Silver Lake	Madison	—	1962	Water Supply	Significant
Monee Lake	Will	—	1900	Recreation	Significant
Borah Lake	Richland	—	1953	Recreation	High
Kinmundy Old Lake	Marion	—	1885	Recreation	Low
Coulterville Lake	Randolph	—	1917	Recreation	Low
Paradise Lake	Pike	—	1997	Debris Control	Low
Charleston Side Channel Lake	Coles	—	1981	Water Supply	Significant
Loveless Lake	Macoupin	—	1981	Water Supply	Significant
Vermont City Lake	McDonough	—	1940	Recreation	Significant

Frequently Asked Questions

How many reservoirs are in Illinois?

67 of 594 measured Illinois lakes (11%) are man-made reservoirs in the USACE National Inventory of Dams. 52 are rated High or Significant hazard, meaning failure would put downstream lives or property at substantial risk. The oldest matched dam dates to 1885.

What's the largest reservoir in Illinois?

The largest matched reservoir in Illinois is Carlyle Lake in Clinton County at 24,580 acres of normal surface area, impounded by the Carlyle Dam - Keyesport Levee (completed 1966).

What's the difference between a reservoir and a natural lake?

A reservoir is a body of water impounded by a man-made dam — typically built for flood control, hydroelectric power, water supply, irrigation, or recreation. A natural lake formed without human intervention, usually from glacial scouring, volcanic activity, or river meandering. Reservoirs typically have shoreline that fluctuates with seasonal water level management, while natural lakes have more stable shorelines. The USACE National Inventory of Dams classifies every regulated dam in the United States, which is how we identify which LakeQuality lakes are actually reservoirs.

What does the hazard class mean?

USACE assigns each dam a hazard potential classification based on what would happen downstream if the dam failed — NOT how likely the dam is to fail. "Low" hazard means dam failure would cause no probable loss of life and only low economic loss. "Significant" means probable loss of life is unlikely but appreciable economic damage would occur. "High" means probable loss of life and significant economic damage. The classification is about consequence, not condition. Many High-hazard dams are perfectly safe; they're rated High because populated areas have grown downstream over time.

Where does this reservoir data come from?

Every reservoir record on this page is matched to the USACE National Inventory of Dams (NID), the federal database of all dams ≥25 ft tall or impounding ≥50 acre-feet, plus any dam that poses a Significant or High hazard regardless of size. The NID is published by the U.S. Army Corps of Engineers and updated annually. Surface area, storage capacity, dam height, and hazard classification come directly from NID records.

Where to stay near Illinois reservoirs

Compare cabins, lodges, and vacation rentals near the largest reservoirs in Illinois — live availability and prices for boating, fishing, and lake trips.

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More on reservoirs and water quality

Are Reservoirs Cleaner Than Natural Lakes?

Dam-built reservoirs and natural lakes compared side by side on the same nutrient and algae measurements — the gap, the reasons behind it, and the exceptions.

Do Deeper Lakes Have Better Water Quality?

Surveyed maximum depth against nutrient and algae readings: the pattern, the shallow lakes that still read clean, and why land use beats bathymetry.

Lake Water Quality Explained: What the Readings Mean

How nutrient and algae readings are read against EPA ecoregion condition classes, what each class means in the water, and why a clean reading is not a clearance.

Why Lakes Turn Green: Phosphorus and Nutrient Pollution

How phosphorus and nutrient runoff drive algae growth and turn lakes green, where the nutrients come from, and what it means for a lake’s readings.

Data source

Reservoir data from the USACE National Inventory of Dams (NID), the federal database of all regulated dams. Dam attributes (height, year completed, storage capacity, hazard class) are matched to LakeQuality lakes by proximity and dam-name similarity. Some lakes may be reservoirs that aren't matched if the dam record uses a name substantially different from our lake name.