
Hardin County Lake Quality
Illinois, 1 lake, average grade D (Nutrient-rich)
Hardin County holds 1 monitored lake. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. Every one of those lake carries an A–F grade, so the county-level summary covers the full set rather than a monitored subset. The county-wide average grade is D — water quality issues are persistent across most of the monitored basins. 0 lakes fall into the F bracket outright.
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 Tecumseh Lake (D); the most-stressed is Tecumseh Lake (D).
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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
1 lake1 graded lake
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | DTecumseh LakeHardin | D | 3.6 ft | 27 µg/L | 22.5 µg/L | No recent samples | Not recorded |
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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 United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.