O Fallon, IL
Lead reported as not detected
Latest 90th-percentile lead: reported as 0 (not detected) (monitoring period 2026-2028). The federal action level is 15 ppb today and drops to 10 ppb in Nov 2027; EPA's health goal is 0. The latest 90th-percentile result was reported as 0 (not detected at the lab's limit). That says the sampled homes were low, not that your home has no lead service line. Check your utility's service line inventory for your address.
Who runs the water here
O Fallon serves about 46,603 people through 18,497 service connections, which makes it a large system under EPA's size classes. It is owned by a local government (city, town, county or district) and draws surface water, in St. Clair County, Illinois. EPA system ID: IL1631100; phone on file: 618-624-4500. Ask them for your address in their service line inventory - every system had to publish one by Oct 2024.
Lead results over time
That is down 2.2 ppb from 2.2 ppb in the period ending 2025. The highest 90th-percentile result EPA holds for O Fallon is 2.2 ppb across 8 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2028 | 0 (not detected) |
| 2025 | 2.2 ppb |
| 2025 | 1.9 ppb |
| 2025 | 0 (not detected) |
| 2025 | 0 (not detected) |
| 2023 | 0 (not detected) |
| 2020 | 2 ppb |
| 2017 | 1 ppb |
Against other Illinois systems
Of the 1,744 Illinois systems with a lead result, the median latest reading is 0 ppb; 22 are over 15 ppb right now and 152 have gone over at some point. O Fallon's reported as 0 (not detected) sits at the 54th percentile in Illinois and the 40th nationally (higher means more lead). Systems reporting 0 tie at the bottom, so the rank mostly reflects size among them.
Nearby utilities
23 other systems share St. Clair County; 8 of them have a higher latest lead result than O Fallon. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Il American-East St Louis | 131,368 | 3 ppb |
| Caseyville | 13,798 | 0 (not detected) |
| Cahokia Heights | 12,528 | 0 (not detected) |
| Mascoutah | 8,759 | 4.9 ppb |
| American Water Oper And Maintenance, Llc | 6,779 | 0 (not detected) |
| Lebanon | 4,714 | 2.1 ppb |
| Freeburg | 4,707 | 1 ppb |
| Dupo | 4,684 | 0 (not detected) |
| Smithton | 4,381 | 0 (not detected) |
| Millstadt | 4,071 | 0 (not detected) |
What to do in your house
Look up your address in O Fallon's service line inventory. If it says lead, galvanized or unknown, test your tap. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask O Fallon whether it covers that cost before hiring anyone - many utilities now do.
These figures describe homes the utility sampled, not your tap. Only your service line record or a test of your own water answers the question for your house. Why sampled homes are the worst-case ones is in the guide to reading the number. Small systems behave differently: why small systems go over more often.