# Counties in Ohio by highest daily Air Quality Index (US EPA), 2001

All 45 values come from U.S. Environmental Protection Agency for 2001, so the places are comparable. 13 counties have no value for that period and are not ranked.

- Indicator id: `aqi_max`
- Unit: index
- Definition: Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: highest daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/highest-daily-air-quality-index/ohio-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Clinton County | 203 |
| 1 | Summit County | 203 |
| 3 | Jefferson County | 202 |
| 3 | Mahoning County | 202 |
| 5 | Ashtabula County | 200 |
| 5 | Hamilton County | 200 |
| 7 | Butler County | 195 |
| 7 | Medina County | 195 |
| 7 | Portage County | 195 |
| 10 | Geauga County | 192 |
| 10 | Madison County | 192 |
| 12 | Lake County | 190 |
| 12 | Lucas County | 190 |
| 12 | Trumbull County | 190 |
| 15 | Franklin County | 187 |
| 15 | Stark County | 187 |
| 17 | Cuyahoga County | 185 |
| 18 | Knox County | 179 |
| 19 | Delaware County | 177 |
| 19 | Miami County | 177 |
| 21 | Fayette County | 174 |
| 21 | Lawrence County | 174 |
| 21 | Noble County | 174 |
| 21 | Washington County | 174 |
| 25 | Montgomery County | 172 |
| 26 | Licking County | 169 |
| 26 | Warren County | 169 |
| 26 | Wood County | 169 |
| 29 | Clark County | 166 |
| 30 | Clermont County | 164 |
| 31 | Crawford County | 161 |
| 31 | Greene County | 161 |
| 31 | Lorain County | 161 |
| 34 | Scioto County | 160 |
| 35 | Allen County | 159 |
| 36 | Preble County | 136 |
| 37 | Athens County | 114 |
| 38 | Wyandot County | 58 |
| 39 | Seneca County | 56 |
| 40 | Monroe County | 54 |
| 41 | Belmont County | 53 |
| 41 | Columbiana County | 53 |
| 43 | Ottawa County | 40 |
| 44 | Hancock County | 38 |
| 45 | Sandusky County | 36 |