Williamson County Lake Quality
Illinois, 1 lakes, average grade C (Fair)
Williamson County has 1 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. Williamson County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.
The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Lake of Egypt (C); the most-stressed is Lake of Egypt (C).
Quick Answers for Williamson County
Planning a trip? Check special fishing regulations for Lake of Egypt — or check the official Illinois fishing regulations.
All Lakes in Williamson County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Lake of Egypt | C | 3.2 ft | 26 µg/L |
Other Counties in Illinois
See how Williamson County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 15 states.
Where to stay near Williamson County
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Source: EPA National Aquatic Resource Surveys, 2026.