Reservoirs in Illinois
71 of 144 graded Illinois lakes (49%) are man-made reservoirs in the USACE National Inventory of Dams. 55 carry a High or Significant hazard rating.
Reading the Illinois reservoir landscape
71 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
All 71 Illinois reservoirs (by surface area)
| Reservoir | County | Grade | Surface area | Year built | Purpose | Hazard |
|---|---|---|---|---|---|---|
| Carlyle Lake | Clinton | F | 24,580 ac | 1966 | Flood Risk Reduction | High |
| Lake Springfield | Sangamon | F | 4,224 ac | 1933 | Recreation | High |
| Decatur Lake | Macon | F | 3,335 ac | 1922 | Recreation | High |
| Kinkaid Lake | Jackson | B | 2,500 ac | 1972 | Recreation | High |
| Lake of Egypt | Williamson | C | 2,265 ac | 1962 | Other | High |
| Lou Yaeger Lake | Montgomery | F | 1,410 ac | 1966 | Recreation | High |
| Mattoon Lake | Cumberland | F | 980 ac | 1957 | Recreation | Significant |
| Governor Bond Lake | Bond | F | 900 ac | 1969 | Recreation | Significant |
| Otter Lake | Macoupin | D | 760 ac | 1969 | Recreation | Significant |
| Raccoon Lake | Marion | F | 730 ac | 1943 | Water Supply | High |
| Sara Lake | Effingham | D | 586 ac | 1957 | Recreation | Significant |
| Jacksonville Lake | Morgan | D | 477 ac | 1939 | Recreation | Significant |
| Holiday Shores Lake | Madison | F | 345 ac | 1965 | Recreation | Significant |
| Centralia Lake | Marion | D | 300 ac | 1911 | Recreation | Significant |
| Mauvaise Terre Lake | Morgan | F | 262 ac | 1923 | Recreation | High |
| Round Lake | Lake | B | 242 ac | 1945 | Recreation | Significant |
| Paradise Lake | Coles | F | 174 ac | 1929 | Recreation | High |
| George Lake | Rock Island | C | 167 ac | 1962 | Recreation | High |
| Kinmundy New Lake | Marion | D | 100 ac | 1998 | Recreation | High |
| Glendale Lake | Pope | B | 84 ac | 1938 | Recreation | Significant |
| Salem Lake | Marion | F | 78 ac | 1912 | Recreation | High |
| Vienna Correctional Center Lake | Johnson | C | 74 ac | 1964 | Recreation | Low |
| Loch Lomond Lake | Lake | A | 72 ac | 1958 | Recreation | Significant |
| Maple Lake | Cook | D | 60 ac | 1918 | Recreation | Significant |
| Nashville City Lake | Washington | F | 52 ac | 1935 | Recreation | High |
| Greenfield Lake | Greene | D | 52 ac | 1959 | Water Supply | Significant |
| Vernor Lake | Richland | D | 45 ac | 1924 | Recreation | Significant |
| Palmyra-Modesto Lake | Macoupin | C | 37 ac | 1965 | Water Supply | Significant |
| Midlothian Lake | Cook | D | 30 ac | 1975 | Flood Risk Reduction | High |
| One Horse Gap Lake | Pope | B | 29 ac | 1973 | Recreation | Significant |
| Pounds Hollow Lake | Gallatin | C | 28 ac | 1939 | Recreation | Significant |
| Fairfield Lake | Wayne | F | 18 ac | 1979 | Water Supply | Low |
| Tecumseh Lake | Hardin | B | 13 ac | 1976 | Recreation | Low |
| Woods Creek Lake | McHenry | C | 9.3 ac | 1926 | Recreation | High |
| Mermet Lake | Massac | D | 0.7 ac | 1950 | Recreation | Low |
| Lake Arlington | Cook | D | — | 1977 | Flood Risk Reduction | High |
| Bull Frog Lake | Cook | F | — | 1958 | Recreation | Significant |
| Papoose Lake | Cook | D | — | 1956 | Recreation | Significant |
| Sauk Lake | Cook | F | — | 1923 | Recreation | Low |
| Doughnut Lake | Cook | D | — | 1987 | Flood Risk Reduction | High |
| Tampier Lake | Cook | F | — | 1964 | Recreation | Significant |
| Lake Calumet | Cook | F | — | 1960 | Navigation | High |
| Silver Lake | McHenry | B | — | 1929 | Recreation | Low |
| Saganashkee Slough Lake | Cook | F | — | 1948 | Recreation | Significant |
| Silver Lake | McHenry | B | — | 1929 | Recreation | Low |
| Bullfrog Lake | Cook | D | — | 1958 | Recreation | Significant |
| Hastings Lake | Lake | D | — | 1955 | Recreation | Low |
| Galena Lake | Jo Daviess | D | — | 1974 | Recreation | High |
| Timber Lake | Lake | B | — | 1949 | Recreation | Low |
| Calumet Lake | Cook | B | — | 1960 | Navigation | High |
| Randolph Lake | Randolph | D | — | 1960 | Recreation | Significant |
| Sam Dale Lake | Wayne | F | — | 1960 | Recreation | Significant |
| Wayne City Lake | Wayne | D | — | 1983 | Water Supply | Low |
| Tampier Lake | Cook | D | — | 1964 | Recreation | Significant |
| Timber Lake | Carroll | B | — | 1960 | Recreation | Significant |
| Bass Lake | Lee | C | — | 1971 | Recreation | Low |
| Woodhaven Lake | Lee | C | — | 1975 | Recreation | Low |
| Shabbona Lake | DeKalb | C | — | 1974 | Other | Low |
| Glenn Shoals Lake | Montgomery | F | — | 1978 | Flood Risk Reduction | Significant |
| Newton Lake | Jasper | D | — | — | Other | Significant |
| Marie Lake | Lake | D | — | — | Debris Control | High |
| Highland Silver Lake | Madison | F | — | 1962 | Water Supply | Significant |
| Monee Lake | Will | D | — | 1900 | Recreation | Significant |
| Borah Lake | Richland | F | — | 1953 | Recreation | High |
| Kinmundy Old Lake | Marion | F | — | 1885 | Recreation | Low |
| Coulterville Lake | Randolph | F | — | 1917 | Recreation | Low |
| Paradise Lake | Pike | F | — | 1997 | Debris Control | Low |
| Charleston Side Channel Lake | Coles | D | — | 1981 | Water Supply | Significant |
| Loveless Lake | Macoupin | D | — | 1981 | Water Supply | Significant |
| Vermont City Lake | McDonough | F | — | 1940 | Recreation | Significant |
| Lake Calumet | Cook | B | — | 1960 | Navigation | High |
Frequently Asked Questions
How many reservoirs are in Illinois?
71 of 144 graded Illinois lakes (49%) are man-made reservoirs in the USACE National Inventory of Dams. 55 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 LakeGrade 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.
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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 LakeGrade 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.