Lakes / Illinois / Franklin County / Mine Number 21 Reservoir
Mine Number 21 Reservoir, Illinois
17,062.04 acres
Surface Area
Where It Sits, and How Deep It Goes
Locator - Illinois
38.11 degrees N, 88.96 degrees W - Franklin County. State and county outlines drawn from Census boundary data; the lake marker is placed by its USGS National Hydrography Dataset coordinates, not by eye. Schematic - not a survey map.
How Mine Number 21 Reservoir Stacks Up
- Ranks #2 for surface area among the Illinois lakes counted so far - 17,062.04 acres.
- The largest lake in Franklin County among those counted.
- About 30 miles from Carbondale, as the crow flies.
Lakes Nearby
| Lake | County | Distance | Surface Area |
|---|---|---|---|
| Lake Benton | Franklin | 4.5 mi | 44.48 acres |
| Raw Water Reservoir | Jefferson | 4.7 mi | 87.97 acres |
| Sesser Lake | Franklin | 4.8 mi | 42.26 acres |
| Lake Hamilton | Franklin | 5.0 mi | 33.11 acres |
| Valier Lake | Franklin | 6.5 mi | 57.32 acres |
| East Lake Impoundment | Jefferson | 7.5 mi | 45.22 acres |
Straight-line distance between lake centers.
Facts and Figures
Questions About Mine Number 21 Reservoir
How Big Is Mine Number 21 Reservoir?
Mine Number 21 Reservoir covers 17,062.04 acres in Franklin County, Illinois.
What Is the Largest Lake in Franklin County?
Mine Number 21 Reservoir is the largest lake in Franklin County, at 17,062.04 acres.
Largest Lakes in Illinois
| # | Lake | County | Surface Area | Max Depth |
|---|---|---|---|---|
| 1 | Carlyle Lake | Clinton | 22,796.77 acres | - |
| 2 | Mine Number 21 Reservoir | Franklin | 17,062.04 acres | - |
| 3 | Upper Peoria Lake | Woodford | 15,460.64 acres | - |
| 4 | Lake Shelbyville | Shelby | 10,235.1 acres | - |
| 5 | Crab Orchard Lake | Williamson | 7,292.57 acres | - |
All 511 Illinois lakes ranked by surface area
Sources: USGS National Hydrography Dataset (The National Map) lake data (ID 120031520). Verified October 30, 2026.