Hardin County Lake Quality
Illinois, 1 lakes, average grade B (Good)
Only 1 lakes in Hardin County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. With an average grade of B, Hardin County sits comfortably above the Illinois median.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Tecumseh Lake (B) is the cleanest in the county.
Quick Answers for Hardin County
Planning a trip? Check special fishing regulations for Tecumseh Lake — or check the official Illinois fishing regulations.
All Lakes in Hardin County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Tecumseh Lake | B | 3.6 ft | 18 µg/L |
Other Counties in Illinois
See how Hardin 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 Hardin County
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Source: EPA National Aquatic Resource Surveys, 2026.