Updated August 2026 · All 3 lakes with a surveyed depth
Deepest Inland Lake in Illinois: Devils Kitchen Lake
Devils Kitchen Lake is Illinois's deepest inland lake, per the Illinois Office of Tourism (State of Illinois); fishery co-managed by Illinois DNR and USFWS. Great Lake; Illinois' Lake Michigan waters are far deeper than anything inland. Devils Kitchen is the deepest lake entirely inside Illinois. Published depths for Devils Kitchen Lake differ between sources; the agency's figure is 90 ft, so no single number is settled. Mapped and ranked below: the 3 deepest of 3 Illinois lakes with a surveyed maximum depth.
Top 3 Deepest Lakes in Illinois (by max depth)
| # | Lake | County | Max depth | Mean depth | Surface area |
|---|---|---|---|---|---|
| 1 | Citizens Lake | Warren | 33 ft | — | 25 ac |
| 2 | Pearl Lake | Winnebago | 31 ft | — | 31 ac |
| 3 | Frentress Lake | Jo Daviess | 10 ft | — | 132 ac |
Sources and method
- Max and mean depth: state natural-resources agency lake surveys and USACE National Inventory of Dams reservoir records. Surveyed depths only; modeled estimates are never ranked. A dash means the survey did not record a mean.
- Deepest inland lake: Devils Kitchen Lake, per the Illinois Office of Tourism (State of Illinois); fishery co-managed by Illinois DNR and USFWS, 2026-07-30. The agency's figure is 90 ft; other published depths differ, so no single number is treated as settled. Devils Kitchen Lake lake page (its record carries no surveyed depth, so it is not in the table)
- Readings: clarity, phosphorus and chlorophyll-a from the agency's own sampling, shown as reported. Depth is not a water-quality reading.
- Map pins: the 3 table rows with surveyed coordinates. No other lakes are plotted.
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Frequently Asked Questions
What is the deepest lake in Illinois?
Devils Kitchen Lake, in Williamson County, is the deepest inland lake. Great Lake; Illinois' Lake Michigan waters are far deeper than anything inland. Devils Kitchen is the deepest lake entirely inside Illinois. Published depths differ between sources; the agency's figure is 90 ft, so no single number is settled. Source: Illinois Office of Tourism (State of Illinois); fishery co-managed by Illinois DNR and USFWS, 2026-07-30.
How are lake depths measured?
Maximum depth is the deepest point at full-pool water level, from state agency bathymetric surveys and, for reservoirs, dam-design records. The ranking uses surveyed depths only, never modeled estimates. Everyday water level can sit below the surveyed figure during drawdowns or drought. Mean depth, the average across the whole basin, is listed where a survey recorded it.
Why are some Illinois lakes so much deeper than others?
Lake depth depends on how the lake formed. Glacial lakes (common in MN, WI, MI, NY) were carved by ice sheets and can exceed 200 ft. Reservoir lakes (common in IA, MO, OK, KS) are shaped by river valley depth at the dam site — typically 50-150 ft at the dam, much shallower upstream. Flooded mine pits can be deeper still. Oxbow lakes and pothole lakes formed by river meandering or glacial pitting tend to be shallower, usually under 30 ft.
Does deeper mean cleaner?
Not directly, but deeper lakes tend to be cleaner on average. Depth creates thermal stratification in summer, isolating cold deep water from surface algal blooms. Deep lakes also resist nutrient resuspension from wind-driven sediment mixing. That said, many deep lakes still suffer from impairment if the watershed loads heavy phosphorus — each lake's page carries its nutrient readings and EPA impairment status.
What's the average depth of Illinois lakes in this ranking?
Across the 3 deepest Illinois lakes, the average maximum depth is 25 ft and the median is 31 ft (Pearl Lake). This is the top of 3 lakes with a surveyed depth, so it is biased toward deep lakes; the typical Illinois lake is shallower.
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